Semiconductor device

ABSTRACT

To prevent damage on an element even when a voltage high enough to break the element is input. A semiconductor device of the invention operates with a first voltage and includes a protection circuit which changes the value of the first voltage when the absolute value of the first voltage is higher than a reference value. The protection circuit includes: a control signal generation circuit generating a second voltage based on the first voltage and outputting the generated second voltage; and a voltage control circuit. The voltage control circuit includes a transistor which has a source, a drain, and a gate, and which is turned on or off depending on the second voltage input to the gate and thus controls whether the value of the first voltage is changed based on the amount of current flowing between the source and the drain. The transistor also includes an oxide semiconductor layer.

TECHNICAL FIELD

One embodiment of the present invention relates to a semiconductordevice.

BACKGROUND ART

In recent years, semiconductor devices have been developed which arecapable of supplying (also referred to as feeding) power (also referredto as a power supply voltage) through wireless communication, andfurther capable of transmitting and receiving data (also referred to asdata communication) through wireless communication. For example, if afeeding function through wireless communication can be added to aportable information medium (e.g., a cellular phone) which is an exampleof the semiconductor devices, the portable information medium does notneed to be connected to an external power feeding portion and can be fedmore easily, for example, in any environment.

An individual identification technology utilizing an RFID (radiofrequency identification) tag is known as an example of semiconductordevices capable of data transmission, data reception, data storing, dataerasing and the like through wireless communication. The RFID tag isalso referred to as an RF tag, a wireless tag, an electronic tag, or awireless chip. The RFID tag is also referred to as an IC tag, an ICchip, or an IC card because it includes a functional circuit such as anintegrated circuit (IC) for executing authentication or otherprocessing. Data communication with the semiconductor device isperformed by using a wireless communication device (such as areader/writer, which is capable of transmitting and receiving a datasignal through wireless communication). The individual identificationtechnology using the semiconductor device is used for the production,management, or the like of an individual object and has been expected tobe applied to personal authentication.

In general, the semiconductor device does not include in itself a powergenerating means and is fed through wireless communication; thus, thesemiconductor device can be fed even at a distance from a feeding means.The distance over which wireless communication is possible is alsoreferred to as a communication distance. In a semiconductor deviceexternally supplied with power, the feeding efficiency generally tendsto decrease as the communication distance increases. Therefore,semiconductor devices to which a desired amount of power can be suppliedeven at a long communication distance have been researched and developed(see Patent Document 1).

REFERENCE Patent Document [Patent Document 1] Japanese Published PatentApplication No. 2006-005651 DISCLOSURE OF INVENTION

In the case of a semiconductor device capable of wireless communicationover a predetermined distance or longer, however, when the semiconductordevice is fed at a distance shorter than the predetermined distance, avoltage (also referred to as an overvoltage) high enough to break anelement is input to the semiconductor device in some cases.

An object of one embodiment of the present invention is to preventdamage on an element even when a voltage high enough to break theelement is input through wireless communication.

One embodiment of the present invention includes a protection circuitagainst voltage, so that when a voltage high enough to break an elementis input, the voltage applied to the element is reduced by using theprotection circuit to prevent damage on the element.

One embodiment of the present invention is a semiconductor deviceoperating with a first voltage and including a protection circuit whichchanges the value of the first voltage when the absolute value of thefirst voltage is higher than a reference value. The protection circuitincludes: a control signal generation circuit which generates a secondvoltage in accordance with the first voltage and outputs the generatedsecond voltage; and a voltage control circuit. The voltage controlcircuit includes a transistor which has a source, a drain, and a gate,and which is turned on or off depending on the second voltage input as acontrol signal to the gate and thus controls whether the value of thefirst voltage is changed in accordance with the amount of currentflowing between the source and the drain. The transistor also includesan oxide semiconductor layer serving as a channel formation layer. Theband gap of the oxide semiconductor layer is equal to or more than 2 eV.

One embodiment of the present invention is a semiconductor deviceincluding: a rectifier circuit to which a first voltage is input, andwhich rectifies the first voltage to generate a second voltage andoutputs the generated second voltage; and a protection circuit which hasa control signal generation circuit and a voltage control circuit. Thecontrol signal generation circuit includes a divider circuit whichdivides the second voltage to generate a third voltage with use of thedivided voltage and outputs the generated third voltage. The voltagecontrol circuit includes a transistor which has a source, a drain, and agate, and which is turned on or off depending on the third voltage inputas a control signal to the gate and thus controls whether the value ofthe first voltage is changed in accordance with the amount of currentflowing between the source and the drain. The transistor also includesan oxide semiconductor layer serving as a channel formation layer. Theband gap of the oxide semiconductor layer is equal to or more than 2 eV.

One embodiment of the present invention is a semiconductor deviceincluding: an antenna circuit which receives a carrier wave to generatea first voltage and outputs the generated first voltage; a rectifiercircuit to which the first voltage is input, and which rectifies thefirst voltage to generate a second voltage and outputs the generatedsecond voltage; a protection circuit; and a power supply voltagegeneration circuit which generates a power supply voltage in accordancewith the second voltage. The protection circuit includes a controlsignal generation circuit and a voltage control circuit. The controlsignal generation circuit includes a divider circuit which divides thesecond voltage to generate a third voltage with use of the dividedvoltage and outputs the generated third voltage. The voltage controlcircuit includes a transistor which has a source, a drain, and a gate,and which is turned on or off depending on the third voltage input as acontrol signal to the gate and thus controls whether the value of thefirst voltage is changed in accordance with the amount of currentflowing between the source and the drain. The transistor also includesan oxide semiconductor layer serving as a channel formation layer. Theband gap of the oxide semiconductor layer is equal to or more than 2 eV.

One embodiment of the present invention is a semiconductor deviceincluding: an antenna circuit which receives a carrier wave to generatea first voltage and outputs the generated first voltage; a rectifiercircuit to which the first voltage is input, and which rectifies thefirst voltage to generate a second voltage and outputs the generatedsecond voltage; a protection circuit; a power supply voltage generationcircuit which generates a power supply voltage in accordance with thesecond voltage; a demodulation circuit which demodulates the receivedcarrier wave to extract a data signal; a functional circuit to which thedata signal and the power supply voltage are input, and which carriesout processing based on the data signal; and a modulation circuit whichmodulates a carrier wave to be transmitted in accordance with a responsesignal input from the functional circuit. The protection circuitincludes a control signal generation circuit and a voltage controlcircuit. The control signal generation circuit includes a dividercircuit which divides the second voltage to generate a third voltagewith use of the divided voltage and outputs the generated third voltage.The voltage control circuit includes a transistor which has a source, adrain, and a gate, and which is turned on or off depending on the thirdvoltage input as a control signal to the gate and thus controls whetherthe value of the first voltage is changed in accordance with the amountof current flowing between the source and the drain. The transistor alsoincludes an oxide semiconductor layer serving as a channel formationlayer. The band gap of the oxide semiconductor layer is equal to or morethan 2 eV.

Note that in this specification, terms with ordinal numbers, such as“first” and “second”, are used in order to avoid confusion amongcomponents, and the terms do not limit the components numerically.

According to one embodiment of the present invention, damage on anelement can be prevented even in the case where a voltage high enough tobreak the element is input.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram illustrating an example of a configuration ofa semiconductor device in Embodiment 1;

FIGS. 2A and 2B are circuit diagrams each illustrating an example of aconfiguration of a voltage control circuit in Embodiment 1;

FIGS. 3A and 3B are circuit diagrams each illustrating an example of aconfiguration of a control signal generation circuit in Embodiment 2;

FIG. 4 is a circuit diagram illustrating an example of a configurationof a rectifier circuit in Embodiment 3;

FIG. 5 is a diagram illustrating an example of a configuration of asemiconductor device in Embodiment 4;

FIG. 6 is a diagram illustrating an example of a configuration of asemiconductor device in Embodiment 4;

FIG. 7 is a block diagram illustrating an example of a configuration ofa semiconductor device in Embodiment 5;

FIGS. 8A to 8D are cross-sectional schematic diagrams each illustratingan example of a structure of a transistor in Embodiment 6;

FIGS. 9A to 9E are cross-sectional schematic diagrams illustrating anexample of a method for manufacturing a transistor in Embodiment 6;

FIGS. 10A and 10B are cross-sectional schematic diagrams eachillustrating an example of a structure of a plurality of transistors inEmbodiment 7;

FIGS. 11A to 11F are views each illustrating an example of an electronicdevice in Embodiment 8;

FIGS. 12A to 12D are views each illustrating an information medium inEmbodiment 9; and

FIGS. 13A to 13C are graphs each illustrating the transientcharacteristics of a semiconductor device in Example 1.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings. Note that the present invention is notlimited to the following description, and it will be easily understoodby those skilled in the art that various changes and modifications canbe made without departing from the spirit and scope of the presentinvention. Thus, the present invention should not be interpreted asbeing limited to the following description of the embodiments.

Embodiment 1

In this embodiment, a semiconductor device including a protectioncircuit will be described.

First, an example of a configuration of the semiconductor device in thisembodiment will be described with reference to FIG. 1. FIG. 1 is a blockdiagram illustrating an example of the configuration of thesemiconductor device in this embodiment.

The semiconductor device illustrated in FIG. 1 includes a rectifiercircuit (also referred to as a RECT) 101 for rectifying an inputvoltage, and a protection circuit (also referred to as a PRO) 102 forcontrolling the value of the input voltage.

A voltage V21 is input to the rectifier circuit 101. The rectifiercircuit 101 has a function of rectifying the input voltage V21 togenerate a voltage V22, and outputting the generated voltage V22.

The rectifier circuit 101 includes, for example, a rectifier element. Afull-wave rectifier circuit or a half-wave rectifier circuit can be usedas the rectifier circuit 101, for example. Further, an N-fold voltagerectifier circuit (N is a natural number of two or more) can also beused as the rectifier circuit 101. Note that the rectifier circuit 101is not necessarily provided in the semiconductor device in thisembodiment; for example, it does not need to be provided in the casewhere the voltage V21 is a direct-current voltage. In the case where therectifier circuit 101 is not provided, the semiconductor device operateswith the voltage V21.

Note that the voltage V21 is a voltage input through a node N11 and anode N12, and the voltage V22 is a voltage output through a node N13 anda node N12. The node N11, the node N12, and the node N13 are pointsconnected to other elements.

Note that in general, voltage refers to a difference between potentialsat two points (also referred to as a potential difference). However,values of a voltage and a potential are both represented by volt (V) incircuit diagrams and the like in some cases, so that it is difficult todistinguish between them. Thus, in this specification, a potentialdifference between a potential at one point and a potential to be thereference (also referred to as a reference potential) is referred to asa voltage at the point in some cases unless otherwise specified.

The protection circuit 102 has a function of, when the absolute value ofthe voltage V21 is higher than a value to be the reference (alsoreferred to as a reference value), changing the value of the voltage V21input to the rectifier circuit 101 in accordance with the voltage V22rectified by the rectifier circuit 101. The reference value can bedetermined as appropriate depending on the circuit specification. Whenthe absolute value of the voltage V21 is higher than the referencevalue, the value of the voltage V21 is preferably controlled inaccordance with the voltage V22 so as to be equal to or lower than thereference value.

Further, an example of a circuit configuration of the protection circuit102 will be described with reference to FIG. 1.

As illustrated in FIG. 1, the protection circuit 102 includes a controlsignal generation circuit (also referred to as a CTLG) 121 and a voltagecontrol circuit (also referred to as a VCTL) 122.

The control signal generation circuit 121 has a function of generating,in accordance with the voltage V22, a voltage to be a control signalCTL31 of the voltage control circuit 122, and outputting the generatedvoltage.

The voltage output as the control signal CTL31 from the control signalgeneration circuit 121 is input to the voltage control circuit 122. Thevoltage control circuit 122 has a function of controlling whether thevoltage V21 is changed in accordance with the input control signalCTL31.

Configuration examples of the voltage control circuit 122 will bedescribed with reference to FIGS. 2A and 2B. FIGS. 2A and 2B are circuitdiagrams illustrating configuration examples of the voltage controlcircuit in this embodiment.

The voltage control circuit 122 illustrated in FIGS. 2A and 2B includesat least a transistor 122 a.

Note that in this specification, a transistor is a field-effecttransistor and includes at least a source, a drain, and a gate.

The source refers to the entire source electrode and source wiring, orpart of them. In some cases, the source electrode is not distinguishedfrom the source wiring and a conductive layer having the functions ofboth the source electrode and the source wiring is referred to as asource.

The drain refers to the entire drain electrode and drain wiring, or partof them. In some cases, the drain electrode is not distinguished fromthe drain wiring and a conductive layer having the functions of both thedrain electrode and the drain wiring is referred to as a drain.

The gate refers to the entire gate electrode and gate wiring, or part ofthem. In some cases, the gate electrode is not distinguished from thegate wiring and a conductive layer having the functions of both the gateelectrode and the gate wiring is referred to as a gate.

Further, the source and drain of a transistor are switched depending onthe structure, operation conditions, and the like of the transistor;thus, it is difficult to distinguish between the source and the drain.Therefore, in this document (such as the specification, claims, anddrawings), one of the source and the drain of a transistor is referredto as a first terminal and the other is referred to as a second terminalin some cases. In the case where the source or the drain is referred toas a first terminal or a second terminal, the gate is sometimes referredto as a third terminal.

The control signal CTL31 is input to a gate of the transistor 122 a andthe transistor 122 a is turned on or off depending on the voltage of theinput control signal CTL31. The voltage control circuit 122 illustratedin FIGS. 2A and 2B has a function of controlling whether the voltage V21is changed in accordance with the amount of current flowing between asource and a drain of the transistor 122 a.

In the voltage control circuit 122 illustrated in FIG. 2A, a firstterminal of the transistor 122 a is electrically connected to the nodeN11 and a second terminal of the transistor 122 a is electricallyconnected to the node N12.

The voltage control circuit 122 illustrated in FIG. 2B includes acapacitor 122 b.

Note that in this specification, a capacitor includes a first terminaland a second terminal, and includes a first electrode serving as part orthe whole of the first terminal, a second electrode serving as part orthe whole of the second terminal, and a dielectric layer in whichelectric charge is accumulated when voltage is applied between the firstelectrode and the second electrode.

A first terminal of the capacitor 122 b is electrically connected to thenode N11. The capacitor 122 b allows reducing the voltage appliedbetween the source and the drain of the transistor 122 a. A resistor maybe provided instead of the capacitor 122 b.

Note that in this specification, a resistor includes a first terminaland a second terminal.

In the voltage control circuit 122 illustrated in FIG. 2B, the firstterminal of the transistor 122 a is electrically connected to the secondterminal of the capacitor 122 b and the second terminal of thetransistor 122 a is electrically connected to the node N12.

Next, a structure of the transistor which can be used as the transistor122 a will be described below.

As the transistor 122 a, a transistor including an oxide semiconductorlayer which serves as a channel formation layer can be used for example.The oxide semiconductor layer of the transistor, which has a function ofthe channel formation layer, is highly purified to be an intrinsic (alsoreferred to as an I-type) or substantially intrinsic semiconductorlayer.

Note that the high purification means at least one of the followingconcepts: removal of hydrogen from an oxide semiconductor layer as muchas possible; and reduction of defects, which are caused by oxygendeficiency in an oxide semiconductor layer, by supply of oxygen to theoxide semiconductor layer.

As an oxide semiconductor which can be used for the oxide semiconductorlayer, for example, a four-component metal oxide, a three-componentmetal oxide, or a two-component metal oxide can be given. As thefour-component metal oxide, for example, an In—Sn—Ga—Zn—O-based metaloxide can be used. As the three-component metal oxide, for example, anIn—Ga—Zn—O-based metal oxide, an In—Sn—Zn—O-based metal oxide, anIn—Al—Zn—O-based metal oxide, a Sn—Ga—Zn—O-based metal oxide, anAl—Ga—Zn—O-based metal oxide, or a Sn—Al—Zn—O-based metal oxide can beused. As the two-component metal oxide, for example, an In—Zn—O-basedmetal oxide, a Sn—Zn—O-based metal oxide, an Al—Zn—O-based metal oxide,a Zn—Mg—O-based metal oxide, a Sn—Mg—O-based metal oxide, anIn—Mg—O-based metal oxide, or an In—Sn—O-based metal oxide can be used.In addition, an In—O-based metal oxide, a Sn—O-based metal oxide, aZn—O-based metal oxide, or the like can also be used as the oxidesemiconductor. The metal oxide that can be used as the oxidesemiconductor may contain SiO₂.

Moreover, a material represented by InMO₃(ZnO)_(m) (m>0) can be used asthe oxide semiconductor. Here, M denotes one or more of metal elementsselected from Ga, Al, Mn, and Co. For example, M can be Ga, Ga and Al,Ga and Mn, or Ga and Co. For example, an oxide semiconductor whosecomposition formula is represented by InMO₃ (ZnO)_(m) where M is Ga isreferred to as the In—Ga—Zn—O-based oxide semiconductor described above,

Furthermore, the band gap of the oxide semiconductor layer is equal toor more than 2 eV, preferably equal to or more than 2.5 eV, and morepreferably equal to or more than 3 eV, which reduces the number ofcarriers generated by thermal excitation to a negligible level. Inaddition, the amount of impurity such as hydrogen which might serve as adonor is reduced to a certain amount or less so that the carrierconcentration is less than 1×10¹⁴/cm³, preferably equal to or less than1×10¹²/cm³. That is, the carrier concentration of the oxidesemiconductor layer is reduced to zero or substantially zero.

In the aforementioned oxide semiconductor layer, the avalanche breakdowndoes not easily occur and the withstand voltage is high. For example,the band gap of silicon is as narrow as 1.12 eV; thus, electrons areeasily generated due the avalanche breakdown, and the number ofelectrons which are accelerated to high speed so as to go over an energybarrier to a gate insulating layer is increased. In contrast, since theoxide semiconductor used for the aforementioned oxide semiconductorlayer has a band gap of 2 eV or more which is wider than that ofsilicon, the avalanche breakdown does not easily occur and resistance tohot-carrier degradation is higher than that of silicon, and thewithstand voltage is thus high.

The hot-carrier degradation means, for example, deterioration oftransistor characteristics caused by fixed charge which is generatedwhen highly-accelerated electrons are injected into a gate insulatinglayer in the vicinity of a drain in a channel; or deterioration oftransistor characteristics caused by a trap level which is formed at theinterface of a gate insulating layer by highly-accelerated electrons.The deterioration of transistor characteristics is, for example,variations in threshold voltage or gate leakage. The hot-carrierdegradation is caused by channel-hot-electron injection (also referredto as CHE injection) or drain-avalanche-hot-carrier injection (alsoreferred to as DAHC injection).

Note that the band gap of silicon carbide, which is one of materialshaving high withstand voltage, is substantially equal to that of anoxide semiconductor used for the oxide semiconductor layer, butelectrons are less likely to be accelerated in an oxide semiconductorbecause the mobility of the oxide semiconductor is lower than that ofsilicon carbide by approximately two orders of magnitude. Further, anenergy barrier between an oxide semiconductor and a gate insulatinglayer is larger than a barrier between silicon carbide, gallium nitride,or silicon and a gate insulating layer; therefore, the number ofelectrons injected into the gate insulating layer is extremely small,whereby hot-carrier degradation is less likely to be caused andwithstand voltage is higher than in the case of silicon carbide, galliumnitride, or silicon. The oxide semiconductor has a high withstandvoltage even in an amorphous state.

Furthermore, the transistor including the oxide semiconductor layer canhave an off-current per micrometer of channel width of 10 aA/μm (1×10⁻¹⁷A/μm) or less, 1 aA/μm (1×10⁻¹⁸ A/μm) or less, 10 zA/μm (1×10⁻²⁰ A/μm)or less, and further 1 zA/μm (1×10⁻²¹ A/μm) or less.

As illustrated in FIGS. 2A and 2B, an example of the voltage controlcircuit in this embodiment includes at least a transistor. A controlsignal is input to a gate of the transistor from a control signalgeneration circuit and the transistor is turned on depending on theinput control signal, whereby the value of a voltage (the voltage V21)input to the semiconductor device in this embodiment is changed inaccordance with the amount of current flowing between a source and adrain of the transistor.

In addition, the transistor includes an oxide semiconductor layer whichuses an oxide semiconductor having a higher withstand voltage than, forexample, silicon used for a conventional transistor. Damage on aprotection circuit can be prevented by using the transistor for thesemiconductor device in this embodiment, resulting in an increase inreliability.

Next, an example of the operation of the semiconductor deviceillustrated in FIG. 1 will be described.

First, the voltage V21 is input to the rectifier circuit 101 through thenode N11 and the node N12.

In the rectifier circuit 101, the input voltage V21 is rectified so thatthe voltage V22 is generated, and then, the generated voltage V22 isoutput as an output voltage through the node N13 and the node N12.

In the protection circuit 102, the control signal generation circuit 121generates a voltage based on the value of the voltage V22, and thegenerated voltage is output as a control signal CTL31 to the gate of thetransistor 122 a in the voltage control circuit 122.

At this time, the transistor 122 a is turned off when the absolute valueof the voltage V22 is equal to or lower than a reference value.

In the case where the absolute value of the voltage V22 is higher thanthe reference value, the transistor 122 a is turned on and electricalconduction is established between the source and the drain of thetransistor 122 a, so that a current flows between the source and thedrain of the transistor 122 a and the value of the voltage V21 ischanged accordingly. The amount of change of the voltage V21 isdetermined in accordance with the amount of current flowing between thesource and the drain of the transistor 122 a. In other words, the amountof change of the voltage V21 is determined depending on the value of thevoltage V22.

As described above, the example of the semiconductor device shown inthis embodiment includes a protection circuit against voltage, so thatwhen the absolute value of an output voltage is higher than thereference value, the value of an input voltage is changed in accordancewith the output voltage by using the protection circuit. As a result,damage on an element can be prevented even in the case where, forexample, the value of the input voltage is so high at a certain timethat the element is broken. In addition, when the absolute value of theoutput voltage is higher than the reference value, the input voltage canbe controlled so that the output voltage is converged to a constantvalue.

In the example of the semiconductor device shown in this embodiment, theprotection circuit includes a transistor for controlling a change in thevalue of an input voltage, and the transistor includes an oxidesemiconductor layer which serves as a channel formation layer and has awide band gap. Since the transistor has a higher withstand voltage thana conventional transistor and is less likely to be damaged, thereliability of the semiconductor device can be improved. Further, thetransistor has a low off-current, which prevents a decrease in the inputvoltage of the semiconductor device due to the off-current of thetransistor.

Embodiment 2

In this embodiment, an example of a configuration of the control signalgeneration circuit shown in the above Embodiment 1 will be described.

The example of the configuration of the control signal generationcircuit in this embodiment will be described with reference to FIGS. 3Aand 3B. FIGS. 3A and 3B are circuit diagrams illustrating examples ofthe configuration of the control signal generation circuit in thisembodiment.

The control signal generation circuit 121 illustrated in FIG. 3Aincludes at least a divider circuit 201.

The divider circuit 201 has a function of dividing the voltage V22. Anexample of a configuration of the divider circuit 201 will be describedbelow.

The divider circuit 201 includes a resistor 211, a rectifier element 212a, a rectifier element 212 b, a rectifier element 212 c, and a rectifierelement 212 d. Although the control signal generation circuit 121illustrated in FIG. 3A includes the four rectifier elements, the presentinvention is not limited to this example; the control signal generationcircuit of this embodiment can include one rectifier element, or K (K isa natural number of two or more) rectifier elements which areelectrically connected in series to each other in a forward direction.

The rectifier elements 212 a to 212 d are electrically connected inseries to each other in a forward direction.

As the rectifier elements 212 a to 212 d, for example, a PN diode, a PINdiode, or a diode-connected field-effect transistor can be used.

A first terminal of the resistor 211 is electrically connected to acathode of the rectifier element 212 d. Note that a point at which theresistor 211 and the rectifier element 212 d are connected is alsoreferred to as a node N14.

In the divider circuit 201, the voltage V22 is applied between an anodeof the rectifier element 212 a and a second terminal of the resistor211.

Next, an example of the operation of the control signal generationcircuit illustrated in FIG. 3A will be described.

First, the voltage V22 is divided by the divider circuit 201, wherebythe voltage of the node N14 becomes equal to the divided voltage V22.Note that the value of the voltage of the node N14 is determined by thevalue of the voltage V21 and the value of the voltage V22.

For example, when the absolute value of the voltage V21 is equal to orlower than a reference value, any of the rectifier elements 212 a to 212d is brought into a non-conduction state. At this time, the combinedresistance of the rectifier elements 212 a to 212 d can be thought to bemuch higher than the resistance of the resistor 211; accordingly, thevoltage of the node N14 is close to the potential of the node N12. Notethat the reference value is determined as appropriate by controlling thethreshold voltage of the rectifier elements 212 a to 212 d, theresistance of the resistor 211, or the like.

When the absolute value of the voltage V21 is higher than the referencevalue, the rectifier elements 212 a to 212 d are brought into aconduction state. At this time, the combined resistance of the rectifierelements 212 a to 212 d can be thought to be much lower than theresistance of the resistor 211; accordingly, the voltage of the node N14increases. At this time, the voltage of the node N14 becomes equal to orhigher than a value necessary for the transistor 122 a illustrated inFIG. 2A or FIG. 2B to be turned on.

Further, the control signal generation circuit illustrated in FIG. 3Aoutputs the voltage of the node N14 as the control signal CTL31 to thegate of the transistor 122 a illustrated in FIG. 2A or FIG. 2B. That isan example of the operation of the control signal generation circuitillustrated in FIG. 3A.

As illustrated in the example of FIG. 3A, the control signal generationcircuit shown in Embodiment 1 can be formed by using at least a dividercircuit to divide a voltage applied to the divider circuit, andgenerating a control signal of the voltage control circuit shown inEmbodiment 1 with use of the divided voltage.

The control signal generation circuit illustrated in FIG. 3A can have aconfiguration in which all the transistors have the same conductivitytype. Consequently, the number of steps can be reduced as compared tothe case of using a plurality of transistors with different conductivitytypes, resulting in a reduction in manufacturing cost.

Note that the configuration of the control signal generation circuit ofthis embodiment is not limited to that illustrated in FIG. 3A, and canbe other configurations. Another configuration of the control signalgeneration circuit of this embodiment will be described with referenceto FIG. 3B.

The control signal generation circuit 121 illustrated in FIG. 3Bincludes a divider circuit 202, a transistor 203, and a resistor 204.

The divider circuit 202 has a function of dividing the voltage V22. Anexample of a configuration of the divider circuit 202 will be describedbelow.

The divider circuit 202 includes a resistor 221, a rectifier element 222a, a rectifier element 222 b, a rectifier element 222 c, and a rectifierelement 222 d. Although the control signal generation circuit 121illustrated in FIG. 3B includes the four rectifier elements, the presentinvention is not limited to this example; the control signal generationcircuit of this embodiment can include one rectifier element, or Krectifier elements which are electrically connected in series to eachother in a forward direction.

The rectifier elements 222 a to 222 d are electrically connected inseries to each other in a forward direction. An anode of the rectifierelement 222 a is electrically connected to a second terminal of theresistor 221.

As the rectifier elements 222 a to 222 d, for example, a PN diode, a PINdiode, or a diode-connected field-effect transistor can be used.

In the divider circuit 202, the voltage V22 is applied between a firstterminal of the resistor 221 and a cathode of the rectifier element 222d.

In the control signal generation circuit illustrated in FIG. 3B, thevoltage V22 is applied between a first terminal of the transistor 203and a second terminal of the resistor 204.

A gate of the transistor 203 is electrically connected to the secondterminal of the resistor 221.

As the transistor 203, for example, a transistor including a singlecrystal semiconductor can be used.

A first terminal of the resistor 204 is electrically connected to asecond terminal of the transistor 203. Note that a point at which thefirst terminal of the resistor 204 is connected to the second terminalof the transistor 203 is also referred to as a node N16.

Next, an example of the operation of the control signal generationcircuit illustrated in FIG. 3B will be described. Note that as anexample, a p-type transistor is used as the transistor 203.

First, the voltage V22 is divided by the divider circuit 202, wherebythe voltage of a node N15 becomes equal to the divided voltage V22. Notethat the voltage of the node N15 is determined by the value of thevoltage V21 and the value of the voltage V22.

For example, when the absolute value of the voltage V21 is equal to orlower than a reference value, any of the rectifier elements 222 a to 222d is brought into a non-conduction state. At this time, the combinedresistance of the rectifier elements 222 a to 222 d can be thought to bemuch higher than the resistance of the resistor 221; accordingly, thevoltage of the node N15 is close to the potential of the node N11. Notethat the reference value is determined as appropriate by controlling thethreshold voltage of the rectifier elements 222 a to 222 d, theresistance of the resistor 221, or the like.

When the absolute value of the voltage V22 is equal to or lower than thereference value, the transistor 203 is turned off. At this time, thevoltage of the node N16 is substantially equal to the potential of thenode N12.

When the absolute value of the voltage V22 is higher than the referencevalue, the rectifier elements 222 a to 222 d are brought into aconduction state. At this time, the combined resistance of the rectifierelements 222 a to 222 d can be thought to be much lower than theresistance of the resistor 221; accordingly, the voltage of the node N15decreases to a value necessary for the transistor 203 to be turned on.

In addition, when the absolute value of the voltage V22 is higher thanthe reference value, the transistor 203 is turned on and the voltage ofthe node N16 increases. At this time, the voltage of the node N16becomes equal to or higher than a value necessary for the transistor 122a illustrated in FIG. 2A or FIG. 2B to be turned on.

Further, the control signal generation circuit illustrated in FIG. 3Boutputs the voltage of the node N16 as the control signal CTL31 to thegate of the transistor 122 a illustrated in FIG. 2A or FIG. 2B. That isan example of the operation of the control signal generation circuitillustrated in FIG. 3B.

The control signal generation circuit illustrated in FIG. 3B includesthe transistor and the resistor in addition to the configuration of thecontrol signal generation circuit illustrated in FIG. 3A. Theconfiguration including the transistor makes it possible to reduce thetime for the voltage as the control signal CTL31 to change to a desiredvalue.

Note that this embodiment can be combined with or replaced by any of theother embodiments, as appropriate.

Embodiment 3

In this embodiment, an example of the rectifier circuit shown in theabove Embodiment 1 will be described.

First, the example of the configuration of the rectifier circuit in thisembodiment will be described with reference to FIG. 4. FIG. 4 is acircuit diagram illustrating the example of the configuration of therectifier circuit in this embodiment.

The rectifier circuit illustrated in FIG. 4 includes a rectifier element111, a rectifier element 112, and a capacitor 113.

A cathode of the rectifier element 112 is electrically connected to ananode of the rectifier element 111.

A first terminal of the capacitor 113 is electrically connected to acathode of the rectifier element 111.

In the rectifier circuit illustrated in FIG. 4, the voltage V21 isapplied between the node N11 and the node N12, and the voltage V22 isapplied between the node N13 and the node N12.

As the rectifier elements 111 and 112, for example, a PN diode, a PINdiode, or a diode-connected field-effect transistor can be used.

Next, an example of the operation of the rectifier circuit illustratedin FIG. 4 will be described.

When the voltage V21 is higher than a reference potential and theabsolute value of a voltage applied to the rectifier element 111 in aforward direction is higher than the threshold voltage of the rectifierelement 111, the rectifier element 111 is brought into a conductionstate and the rectifier element 112 is brought into a non-conductionstate. At this time, the voltage V21 is rectified by the rectifierelement 111 and a charge corresponding to the potential of the node N11is accumulated in the first terminal of the capacitor 113.

When the voltage V21 is lower than the reference potential and theabsolute value of a voltage applied to the rectifier element 112 in aforward direction is higher than the threshold voltage of the rectifierelement 112, the rectifier element 112 is brought into a conductionstate and the rectifier element 111 is brought into a non-conductionstate. At this time, the voltage V21 is rectified by the rectifierelement 112 and a charge corresponding to the potential of the node N11is accumulated in a second terminal of the capacitor 113. Consequently,a voltage applied to the capacitor 113 increases to about twice as highas the voltage V21. The increased voltage becomes the voltage V22.

As illustrated in the example of FIG. 4, a half-wave voltage doublerrectifier circuit can be used as the rectifier circuit in Embodiment 1.The rectifier circuit is not limited to this example; an N-fold voltagerectifier circuit can be used, and a full-wave rectifier circuit canalso be used.

Note that this embodiment can be combined with or replaced by any of theother embodiments, as appropriate.

Embodiment 4

In this embodiment, a semiconductor device capable of generating a powersupply voltage through wireless communication will be described as anexample of the semiconductor devices shown in the above embodiments.

First, an example of a configuration of the semiconductor device in thisembodiment will be described with reference to FIG. 5 and FIG. 6. FIG. 5and FIG. 6 are diagrams illustrating examples of the configuration ofthe semiconductor device in this embodiment.

The semiconductor device illustrated in FIG. 5 and FIG. 6 includes anantenna circuit 501 which transmits and receives a carrier wave, arectifier circuit 502 which rectifies an input voltage, a protectioncircuit 503 which controls the value of the input voltage, and a powersupply voltage generation circuit (also referred to as a PWRG) 504 whichgenerates a power supply voltage Vp in accordance with the inputvoltage.

The antenna circuit 501 has a function of receiving a carrier wave, andincludes an antenna 511 and a capacitor 512 as illustrated in FIG. 5 andFIG. 6.

The carrier wave is an alternate-current signal which is also referredto as a carrier. With the carrier wave, feeding or data signalcommunication is performed. Note that a carrier wave externallytransmitted to the antenna circuit 501 includes a modulated carrier wave(a modulated wave).

The antenna 511 includes a first terminal and a second terminal.

The capacitor 512 has a function of a resonance capacitor. Although thecapacitor 512 is not necessarily provided in the semiconductor device inthis embodiment, the resonance frequency of the antenna circuit 501 canbe controlled by using the capacitor 512.

In the semiconductor device illustrated in FIG. 5 and FIG. 6, acapacitor 505 is provided between the antenna circuit 501 and therectifier circuit 502. A first terminal of the capacitor 505 iselectrically connected to the first terminal of the antenna 511. Thecapacitor 505 has a function of a filter element which removes a DCcomponent from an output voltage of the antenna circuit 501. Note that apoint at which the first terminal of the capacitor 505 is connected tothe first terminal of the antenna 511 is also referred to as a node N51.

The rectifier circuit 502 includes a transistor 521, a transistor 522,and a capacitor 523.

A first terminal of the transistor 521 is electrically connected to asecond terminal of the capacitor 505, and a second terminal of thetransistor 521 is electrically connected to the power supply voltagegeneration circuit 504. Since a gate of the transistor 521 iselectrically connected to the first terminal of the transistor 521, thetransistor 521 has a function of a rectifier element. Note that a pointat which the first terminal of the transistor 521 is connected to thesecond terminal of the capacitor 505 is also referred to as a node N53.

A first terminal of the transistor 522 is electrically connected to thefirst terminal of the transistor 521, and a second terminal of thetransistor 522 is electrically connected to the second terminal of theantenna 511. Since a gate of the transistor 522 is electricallyconnected to the second terminal of the transistor 522, the transistor522 has a function of a rectifier element.

As the transistor 521 and the transistor 522, it is possible to use, forexample, a transistor including an oxide semiconductor layer which canbe applied to the transistor 122 a illustrated in FIG. 2A or FIG. 2B.

A first terminal of the capacitor 523 is electrically connected to thesecond terminal of the transistor 521, and a second terminal of thecapacitor 523 is electrically connected to the second terminal of theantenna 511.

The protection circuit 503 includes a resistor 531, a transistor 532 a,a transistor 532 b, a transistor 532 c, a transistor 532 d, a transistor533, a resistor 534, a capacitor 535, and a transistor 536.

A first terminal of the resistor 531 is electrically connected to thefirst terminal of the capacitor 523. Note that a point at which thefirst terminal of the resistor 531 is connected to the first terminal ofthe capacitor 523 is also referred to as a node N54.

A first terminal of the transistor 532 a is electrically connected to asecond terminal of the resistor 531. Since a gate of the transistor 532a is electrically connected to the first terminal of the transistor 532a, the transistor 532 a has a function of a rectifier element. Thetransistor 532 a has n-type conductivity.

A first terminal of the transistor 532 b is electrically connected to asecond terminal of the transistor 532 a. Since a gate of the transistor532 b is electrically connected to the first terminal of the transistor532 b, the transistor 532 b has a function of a rectifier element. Thetransistor 532 b has n-type conductivity.

A first terminal of the transistor 532 c is electrically connected to asecond terminal of the transistor 532 b. Since a gate of the transistor532 c is electrically connected to the first terminal of the transistor532 c, the transistor 532 c has a function of a rectifier element. Thetransistor 532 c has n-type conductivity.

A first terminal of the transistor 532 d is electrically connected to asecond terminal of the transistor 532 c, and a second terminal of thetransistor 532 d is electrically connected to the second terminal of theantenna 511. Since a gate of the transistor 532 d is electricallyconnected to the first terminal of the transistor 532 d, the transistor532 d has a function of a rectifier element. The transistor 532 d hasn-type conductivity.

As the transistors 532 a to 532 d, it is possible to use, for example, atransistor including an oxide semiconductor layer which can be appliedto the transistor 122 a illustrated in FIG. 2A or FIG. 2B.

A first terminal of the transistor 533 is electrically connected to thefirst terminal of the capacitor 523, and a gate of the transistor 533 iselectrically connected to the second terminal of the resistor 531. Notethat a point at which the gate of the transistor 533 is connected to thesecond terminal of the resistor 531 is also referred to as a node N55.The transistor 533 has p-type conductivity.

As the transistor 533, for example, a transistor including a singlecrystal semiconductor can be used.

A first terminal of the resistor 534 is electrically connected to asecond terminal of the transistor 533, and a second terminal of theresistor 534 is electrically connected to the second terminal of theantenna 511. Note that a point at which the first terminal of theresistor 534 is connected to the second terminal of the transistor 533is also referred to as a node N56.

The capacitor 535 has a function of reducing the voltage applied betweena source and a drain of the transistor 536. A first terminal of thecapacitor 535 is electrically connected to the first terminal of theantenna 511.

A first terminal of the transistor 536 is electrically connected to asecond terminal of the capacitor 535, and a second terminal of thetransistor 536 is electrically connected to the second terminal of theantenna 511. Note that the transistor 536 has n-type conductivity.

As the transistor 536, it is possible to use, for example, a transistorincluding an oxide semiconductor layer which can be applied to thetransistor 122 a illustrated in FIG. 2A or FIG. 2B.

The power supply voltage generation circuit 504 has a function ofsmoothing the voltage applied between the node N54 and the node N52,namely, an output voltage of the rectifier circuit 502, and generating apower supply voltage with use of the smoothed voltage. Note that thepower supply voltage generation circuit 504 may have a DC convertercircuit (e.g., a step-up circuit or a step-down circuit), so that theoutput voltage of the rectifier circuit 502 can be converted to adesired voltage with the DC converter circuit and a power supply voltagecan be generated by smoothing the converted voltage.

Further, the semiconductor device illustrated in FIG. 6 includes afilter circuit 506, and the filter circuit 506 includes a resistor 507and a capacitor 508.

A first terminal of the resistor 507 is electrically connected to thesecond terminal of the transistor 533, and a second terminal of theresistor 507 is electrically connected to a gate of the transistor 536.

A first terminal of the capacitor 508 is electrically connected to thesecond terminal of the resistor 507, and a second terminal of thecapacitor 508 is electrically connected to the second terminal of theantenna 511.

Although the filter circuit 506 is not necessarily provided in thesemiconductor device in this embodiment, the filter circuit 506 allowsreducing the noise of a voltage generated in the antenna circuit 501.

Next, an example of the operation of the semiconductor deviceillustrated in FIG. 5 will be described as an example of the operationof the semiconductor device in this embodiment.

First, a carrier wave is received by the antenna 511.

When the antenna 511 receives a carrier wave, a voltage V61 is generatedbetween the node N51 and the node N52 in accordance with the receivedcarrier wave.

Further, a voltage V62 applied between the node N53 and the node N52 ischanged depending on the voltage V61.

The voltage V62 is rectified by the rectifier circuit 502 and arectified voltage V63 is output through the node N54 and the node N52.

Then, the voltage V63 is input to the protection circuit 503.

In the protection circuit 503, the voltage V63 is divided by theresistor 531 and the transistors 532 a to 532 d. At this time, thevoltage of the node N55 becomes equal to the divided voltage V63. Thetransistor 533 is turned on or off depending on the voltage of the nodeN55.

For example, when the absolute value of the voltage of the node N55 isequal to or lower than a reference value, the voltage of the node N55 isclose to the potential of the node N54, whereby the transistor 533 isturned off. At this time, the voltage of the node N56 is substantiallyequal to the potential of the node N52 and the transistor 536 is turnedoff, so that the value of the voltage V61 is not changed substantially.

When the absolute value of the voltage of the node N55 is higher thanthe reference value, the voltage of the node N55 is close to thepotential of the node N52, whereby the transistor 533 is turned on. Atthis time, the voltage of the node N56 is determined by the amount ofcurrent flowing between a source and a drain of the transistor 533, andthe transistor 536 is turned on in accordance with the voltage of thenode N56, so that the value of the voltage V61 is changed. The amount ofchange of the voltage V61 is determined by the amount of current flowingbetween a source and a drain of the transistor 536.

Further, the voltage V63 is input to the power supply voltage generationcircuit 504.

In the power supply voltage generation circuit 504, a power supplyvoltage Vp is generated with use of the input voltage V63, and thegenerated power supply voltage Vp is output. That is an example of theoperation of the semiconductor device illustrated in FIG. 5.

As described above, the example of the semiconductor device in thisembodiment generates a power supply voltage through wirelesscommunication. Since the semiconductor device that is an example of thisembodiment includes a protection circuit, when a power supply voltage isgenerated through wireless communication, damage on an element can beprevented even in the case where a voltage high enough to break theelement is input to the semiconductor device.

Note that this embodiment can be combined with or replaced by any of theother embodiments, as appropriate.

Embodiment 5

In this embodiment, a semiconductor device capable of transmitting andreceiving signals (also referred to as signal communication) throughwireless communication will be described as an example of thesemiconductor devices shown in the above embodiments.

First, an example of a configuration of the semiconductor device in thisembodiment will be described with reference to FIG. 7. FIG. 7 is a blockdiagram illustrating an example of the configuration of thesemiconductor device in this embodiment.

The semiconductor device illustrated in FIG. 7 includes an antennacircuit 701 which transmits and receives a carrier wave, a rectifiercircuit 702 which rectifies an input voltage, a protection circuit 703which controls the value of the input voltage, a power supply voltagegeneration circuit 704 which generates a power supply voltage inaccordance with the input voltage, a demodulation circuit (also referredto as DMOD) 705 which demodulates a voltage signal based on the carrierwave received by the antenna circuit 701, a functional circuit (alsoreferred to as FUNC) 706 which operates with a power supply voltage andcarries out processing based on the voltage signal demodulated by thedemodulation circuit 705, and a modulation circuit (also referred to asMOD) 707 which modulates a carrier wave to be transmitted in accordancewith the response signal.

The antenna circuit 701 has a function of transmitting and receiving acarrier wave.

A voltage based on the carrier wave received by the antenna circuit 701is input to the rectifier circuit 702. The rectifier circuit 702 has afunction of rectifying the voltage.

The voltage rectified by the rectifier circuit 702 is input to theprotection circuit 703. The protection circuit 703 has a function ofcontrolling the value of a voltage input to the rectifier circuit 702 inaccordance with in accordance with the input voltage.

As the rectifier circuit 702 and the protection circuit 703, therectifier circuit and the protection circuit in any of the semiconductordevices shown in the above embodiments can be used.

The voltage rectified by the rectifier circuit 702 is input to the powersupply voltage generation circuit 704. The power supply voltagegeneration circuit 704 has a function of generating a power supplyvoltage Vp in accordance with the input voltage.

The demodulation circuit 705 has a function of demodulating the carrierwave received by the antenna circuit 701 to extract a data signal.

The data signal is input from the demodulation circuit 705 to thefunctional circuit 706. The functional circuit 706 has a function ofcarrying out processing based on the data signal.

The functional circuit 706 includes, for example, a memory in whichspecific data or the like is stored, a memory controller which controlsthe access to the memory, a logic circuit which generates a responsesignal after the processing based on a demodulated signal is carriedout, and an interface which converts the response signal in accordancewith an external apparatus. These circuits operate when the power supplyvoltage Vp is input.

The response signal is input from the functional circuit 706 to themodulation circuit 707. The modulation circuit 707 has a function ofmodulating a carrier wave to be transmitted in accordance with theresponse signal as needed.

Next, an example of the operation of the semiconductor deviceillustrated in FIG. 7 will be described.

First, an externally applied carrier wave is received by the antennacircuit 701.

When the antenna circuit 701 receives a carrier wave, a voltage isgenerated in accordance with the received carrier wave.

The voltage generated in accordance with the carrier wave received bythe antenna circuit 701 is input to the rectifier circuit 702 and thedemodulation circuit 705.

Then, the rectifier circuit 702 rectifies the input voltage and outputsthe rectified voltage.

The output voltage of the rectifier circuit 702 is input to theprotection circuit 703.

When the absolute value of a voltage input to the rectifier circuit 702is equal to or lower than a reference value, the value of a voltageinput from the protection circuit 703 to the rectifier circuit 702 isnot changed substantially.

When the absolute value of the voltage input to the rectifier circuit702 is higher than the reference value, the value of a voltage inputfrom the protection circuit 703 to the rectifier circuit 702 is changed.The amount of change of the voltage input to the rectifier circuit 702at this time is determined by the voltage input to the rectifier circuit702 and the voltage output from the rectifier circuit 702.

The output voltage of the rectifier circuit 702 is input to the powersupply voltage generation circuit 704.

The power supply voltage generation circuit 704 generates a power supplyvoltage Vp in accordance with the input voltage, and outputs thegenerated power supply voltage Vp.

The power supply voltage Vp is input to the functional circuit 706.

The demodulation circuit 705 demodulates the carrier wave input from theantenna circuit 701 to extract a data signal, and outputs the extracteddata signal.

The data signal is input to the functional circuit 706.

The functional circuit 706 operates when the power supply voltage Vp issupplied, and carries out processing based on the data signal; further,generates a response signal as needed and outputs the generated responsesignal.

The response signal is input to the modulation circuit 707.

When the response signal is input to the modulation circuit 707, acarrier wave to be transmitted from the antenna circuit 701 is modulatedas needed in accordance with the response signal. That is an example ofthe operation of the semiconductor device illustrated in FIG. 7.

As illustrated in the example of FIG. 7, the example of thesemiconductor device in this embodiment generates a power supply voltagethrough wireless communication, and further carries out processing basedon a received carrier wave with use of the power supply voltage,generates a response signal as needed, and modulates a carrier wave tobe transmitted in accordance with the response signal as needed. Inaddition, the semiconductor device in this embodiment includes aprotection circuit. In general, when a power supply voltage is generatedthrough wireless communication, a voltage generated by the antennacircuit is considerably changed depending on a communication distance orthe like. Even in such a case, damage on an element can be preventedwith the protection circuit.

Note that this embodiment can be combined with or replaced by any of theother embodiments, as appropriate.

Embodiment 6

In this embodiment, an example of the transistor that can be applied toany of the semiconductor devices shown in the above embodiments will bedescribed.

As a structure of the transistor that can be applied to any of thesemiconductor devices shown in the above embodiments, for example, atop-gate structure or a bottom-gate structure can be used. As thebottom-gate structure, for example, a staggered structure or a planarstructure can be used.

Further, the transistor that can be applied to any of the semiconductordevices shown in the above embodiments may have a structure includingone channel formation region (also referred to as a single-gatestructure), a structure including a plurality of channel formationregions (also referred to as a multi-gate structure), or a structure inwhich two conductive layers are provided over and under a channel regioneach with an insulating layer interposed therebetween (also referred toas a dual-gate structure).

An example of a structure of the transistor in this embodiment will bedescribed with reference to FIGS. 8A to 8D. FIGS. 8A to 8D arecross-sectional schematic diagrams each illustrating an example of thestructure of the transistor in this embodiment.

The transistor illustrated in FIG. 8A is one of bottom-gate transistors,which is also referred to as an inverted staggered transistor.

The transistor illustrated in FIG. 8A includes a conductive layer 401 aserving as a gate electrode, an insulating layer 402 a serving as a gateinsulating layer, an oxide semiconductor layer 403 a serving as achannel formation layer, and a conductive layer 405 a and a conductivelayer 406 a serving as a source or drain electrode.

The conductive layer 401 a is provided over a substrate 400 a, theinsulating layer 402 a is provided over the conductive layer 401 a, theoxide semiconductor layer 403 a is provided over the conductive layer401 a with the insulating layer 402 a interposed therebetween, and theconductive layer 405 a and the conductive layer 406 a are each providedover part of the oxide semiconductor layer 403 a.

Further, in the transistor illustrated in FIG. 8A, an oxide insulatinglayer 407 a is in contact with part of a top surface of the oxidesemiconductor layer 403 a (part of the oxide semiconductor layer 403 aover which the conductive layer 405 a and the conductive layer 406 a arenot provided). A protective insulating layer 409 a is provided over theoxide insulating layer 407 a.

The transistor illustrated in FIG. 8B is a channel protective (alsoreferred to as a channel stop) transistor which is one of thebottom-gate transistors, and is also referred to as an invertedstaggered transistor.

The transistor illustrated in FIG. 8B includes a conductive layer 401 bserving as a gate electrode, an insulating layer 402 b serving as a gateinsulating layer, an oxide semiconductor layer 403 b serving as achannel formation layer, an insulating layer 427 serving as a channelprotective layer, and a conductive layer 405 b and a conductive layer406 b serving as a source or drain electrode.

The conductive layer 401 b is provided over a substrate 400 b, theinsulating layer 402 b is provided over the conductive layer 401 b, theoxide semiconductor layer 403 b is provided over the conductive layer401 b with the insulating layer 402 b interposed therebetween, theinsulating layer 427 is provided over the conductive layer 401 b withthe insulating layer 402 b and the oxide semiconductor layer 403 binterposed therebetween, and the conductive layer 405 b and theconductive layer 406 b are each provided over part of the oxidesemiconductor layer 403 b with the insulating layer 427 interposedtherebetween.

Further, a protective insulating layer 409 b is in contact with a toppart of the transistor illustrated in FIG. 8B.

The transistor illustrated in FIG. 8C is one of the bottom-gatetransistors.

The transistor illustrated in FIG. 8C includes a conductive layer 401 cserving as a gate electrode, an insulating layer 402 c serving as a gateinsulating layer, an oxide semiconductor layer 403 c serving as achannel formation layer, and a conductive layer 405 c and a conductivelayer 406 c serving as a source or drain electrode.

The conductive layer 401 c is provided over a substrate 400 c, theinsulating layer 402 c is provided over the conductive layer 401 c, theconductive layer 405 c and the conductive layer 406 c are provided overpart of the insulating layer 402 c, and the oxide semiconductor layer403 c is provided over the conductive layer 401 c with the insulatinglayer 402 c, the conductive layer 405 c, and the conductive layer 406 cinterposed therebetween.

Further, in the transistor illustrated in FIG. 8C, an oxide insulatinglayer 407 c is in contact with a top surface and a side surface of theoxide semiconductor layer 403 c. In addition, a protective insulatinglayer 409 c is provided over the oxide insulating layer 407 c.

The transistor illustrated in FIG. 8D is one of top-gate transistors.

The transistor illustrated in FIG. 8D includes a conductive layer 401 dserving as a gate electrode, an insulating layer 402 d serving as a gateinsulating layer, an oxide semiconductor layer 403 d serving as achannel formation layer, and a conductive layer 405 d and a conductivelayer 406 d serving as a source or drain electrode.

The oxide semiconductor layer 403 d is provided over a substrate 400 dwith a base layer 447 interposed therebetween, the conductive layer 405d and the conductive layer 406 d are each provided over part of theoxide semiconductor layer 403 d, the insulating layer 402 d is providedover the oxide semiconductor layer 403 d, the conductive layer 405 d,and the conductive layer 406 d, and the conductive layer 401 d isprovided over the oxide semiconductor layer 403 d with the insulatinglayer 402 d interposed therebetween.

Further, in the transistor illustrated in FIG. 8D, the conductive layer405 d is in contact with a wiring layer 436 through an opening portionformed in the insulating layer 402 d, and the conductive layer 406 d isin contact with a wiring layer 437 through an opening portion formed inthe insulating layer 402 d.

As the substrates 400 a to 400 d, for example, a glass substrate such asa barium borosilicate glass substrate or an aluminoborosilicate glasssubstrate can be used.

Alternatively, a substrate formed of an insulator, such as a ceramicsubstrate, a quartz substrate, or a sapphire substrate can be used asthe substrates 400 a to 400 d. Further alternatively, crystallized glasscan be used for the substrates 400 a to 400 d. Still furtheralternatively, a plastic substrate or a semiconductor substrate ofsilicon or the like can be used as the substrates 400 a to 400 d.

The base layer 447 has a function of preventing diffusion of an impurityelement from the substrate 400 d. As the base layer 447, a siliconnitride layer, a silicon oxide layer, a silicon nitride oxide layer, asilicon oxynitride layer, an aluminum oxide layer, or an aluminumoxynitride layer can be used, for example. The base layer 447 can alsobe formed by stacking layers of materials which can be applied to thebase layer 447.

Note that in the transistors illustrated in FIGS. 8A to 8C, a base layermay be provided between the substrate and the conductive layer servingas a gate electrode, as in the transistor illustrated in FIG. 8D.

As the conductive layers 401 a to 401 d, it is possible to use, forexample, a layer of a metal material such as molybdenum, titanium,chromium, tantalum, tungsten, aluminum, copper, neodymium, or scandiumor an alloy material containing any of these materials as a maincomponent. The conductive layers 401 a to 401 d can also be formed bystacking layers of materials which can be applied to the conductivelayers 401 a to 401 d.

As the insulating layers 402 a to 402 d, a silicon oxide layer, asilicon nitride layer, a silicon oxynitride layer, a silicon nitrideoxide layer, an aluminum oxide layer, an aluminum nitride layer, analuminum oxynitride layer, an aluminum nitride oxide layer, or a hafniumoxide layer can be used, for example. The insulating layers 402 a to 402d can also be formed by stacking layers of materials which can beapplied to the insulating layers 402 a to 402 d. The layers of materialswhich can be applied to the insulating layers 402 a to 402 d can beformed by plasma CVD, sputtering, or the like. For example, theinsulating layers 402 a to 402 d can be formed in such a manner that asilicon nitride layer is formed by plasma CVD and a silicon oxide layeris formed over the silicon nitride layer by plasma CVD.

As an oxide semiconductor which can be used for the oxide semiconductorlayers 403 a to 403 d, for example, a four-component metal oxide, athree-component metal oxide, or a two-component metal oxide can begiven. As the four-component metal oxide, for example, anIn—Sn—Ga—Zn—O-based metal oxide can be used. As the three-componentmetal oxide, for example, an In—Ga—Zn—O-based metal oxide, anIn—Sn—Zn—O-based metal oxide, an In—Al—Zn—O-based metal oxide, aSn—Ga—Zn—O-based metal oxide, an Al—Ga—Zn—O-based metal oxide, or aSn—Al—Zn—O-based metal oxide can be used. As the two-component metaloxide, for example, an In—Zn—O-based metal oxide, a Sn—Zn—O-based metaloxide, an Al—Zn—O-based metal oxide, a Zn—Mg—O-based metal oxide, aSn—Mg—O-based metal oxide, an In—Mg—O-based metal oxide, or anIn—Sn—O-based metal oxide can be used. In addition, an In—O-based metaloxide, a Sn—O-based metal oxide, a Zn—O-based metal oxide, or the likecan also be used as the oxide semiconductor. The metal oxide that can beused as the oxide semiconductor may contain SiO₂. Here, for example, theIn—Ga—Zn—O-based metal oxide means an oxide containing at least In, Ga,and Zn, and the composition ratio of the elements is not particularlylimited. The In—Ga—Zn—O-based metal oxide may contain an element otherthan In, Ga, and Zn.

Further, as an oxide semiconductor which can be used for the oxidesemiconductor layers 403 a to 403 d, a metal oxide represented by achemical formula InMO₃(ZnO)_(m) (m>0, and m is not a natural number) canbe used. Here, M denotes one or more of metal elements selected from Ga,Al, Mn, and Co. For example, M can be Ga, Ga and Al, Ga and Mn, or Gaand Co.

As the conductive layers 405 a to 405 d and the conductive layers 406 ato 406 d, a layer of a metal material such as aluminum, chromium,copper, tantalum, titanium, molybdenum, or tungsten or an alloy materialcontaining any of the metal materials as a main component can be used,for example. The conductive layers 405 a to 405 d and the conductivelayers 406 a to 406 d can also be formed by stacking layers of materialswhich can be applied to the conductive layers 405 a to 405 d and theconductive layers 406 a to 406 d.

For example, the conductive layers 405 a to 405 d and the conductivelayers 406 a to 406 d can be formed by stacking a metal layer ofaluminum or copper and a high-melting-point metal layer of titanium,molybdenum, tungsten, or the like. The conductive layers 405 a to 405 dand the conductive layers 406 a to 406 d may have a structure in which ametal layer of aluminum or copper is provided between a plurality ofhigh-melting-point metal layers. Further, when the conductive layers 405a to 405 d and the conductive layers 406 a to 406 d are formed using analuminum layer to which an element that prevents generation of hillocksor whiskers (e.g., Si, Nd, or Si) is added, heat resistance can beincreased.

Alternatively, the conductive layers 405 a to 405 d and the conductivelayers 406 a to 406 d can be formed using a layer containing aconductive metal oxide. As the conductive metal oxide, indium oxide(In₂O₃), tin oxide (SnO₂), zinc oxide (ZnO), an alloy of indium oxideand tin oxide (In₂O₃—SnO₂, abbreviated to ITO), an alloy of indium oxideand zinc oxide (In₂O₃—ZnO), or such a metal oxide material containingsilicon oxide can be used, for example.

Furthermore, another wiring may be formed using the material used toform the conductive layers 405 a to 405 d and the conductive layers 406a to 406 d.

As the wiring layer 436 and the wiring layer 437, a layer of a materialwhich can be applied to the conductive layers 405 a to 405 d and theconductive layers 406 a to 406 d can be used. The wiring layer 436 andthe wiring layer 437 can also be formed by stacking layers of materialswhich can be applied to the wiring layer 436 and the wiring layer 437.

As the insulating layer 427, a layer which can be applied to the baselayer 447 can be used, for example. The insulating layer 427 can also beformed by stacking layers of materials which can be applied to theinsulating layer 427.

As the oxide insulating layer 407 a and the oxide insulating layer 407c, an oxide insulating layer such as a silicon oxide layer can be used.The oxide insulating layer 407 a and the oxide insulating layer 407 ccan also be formed by stacking layers of materials which can be appliedto the oxide insulating layer 407 a and the oxide insulating layer 407c.

As the protective insulating layers 409 a to 409 c, an inorganicinsulating layer such as a silicon nitride layer, an aluminum nitridelayer, a silicon nitride oxide layer, or an aluminum nitride oxide layercan be used, for example. The protective insulating layers 409 a to 409c can also be formed by stacking layers of materials which can beapplied to the protective insulating layers 409 a to 409 c.

Note that in the semiconductor devices in the above embodiments, inorder to reduce surface unevenness due to the transistor of thisembodiment, a planarization insulating layer can be provided over thetransistor (in the case where the transistor includes an oxideinsulating layer or a protective insulating layer, over the transistorwith the oxide insulating layer or the protective insulating layerinterposed therebetween). As the planarization insulating layer, a layerof an organic material such as polyimide, acrylic, or benzocyclobutenecan be used. Alternatively, a layer of a low-dielectric constantmaterial (a low-k material) can be used as the planarization insulatinglayer. The planarization insulating layer can also be formed by stackinglayers of materials which can be applied to the planarization insulatinglayer.

Next, as an example of a method for manufacturing the transistor in thisembodiment, an example of a method for manufacturing the transistorillustrated in FIG. 8A will be described with reference to FIGS. 9A to9E. FIGS. 9A to 9E are cross-sectional schematic diagrams illustratingan example of the manufacturing method of the transistor illustrated inFIG. 8A. Although an example of the manufacturing method of thetransistor illustrated in FIG. 8A will be shown as an example of themethod for manufacturing the transistor in this embodiment, the presentinvention is not limited to this example. For example, as for thecomponents of FIGS. 8B to 8D which have the same designations as thecomponents of FIG. 8A and whose function is at least partly the same asthat of the components of FIG. 8A, description of the example of themanufacturing method of the transistor illustrated in FIG. 8A can bereferred to as appropriate.

First, the substrate 400 a is prepared, and a first conductive film isformed over the substrate 400 a.

A glass substrate is used as an example of the substrate 400 a.

As the first conductive film, a film of a metal material such asmolybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper,neodymium, or scandium, or an alloy material which contains any of themetal materials as a main component can be used. The first conductivefilm can also be formed by stacking layers of materials which can beapplied to the first conductive film.

Next, a first photolithography process is carried out: a first resistmask is formed over the first conductive film, the first conductive filmis selectively etched with use of the first resist mask to form theconductive layer 401 a, and the first resist mask is removed.

Note that in this embodiment, the resist mask may be formed by anink-jet method. Formation of the resist mask by an inkjet method needsno photomask; thus, manufacturing cost can be reduced.

In order to reduce the number of photomasks and steps in thephotolithography process, the etching step may be performed using aresist mask formed with a multi-tone mask. The multi-tone mask is a maskthrough which light is transmitted to have a plurality of intensities. Aresist mask formed with use of the multi-tone mask has a plurality ofthicknesses and further can be changed in shape by etching; therefore,the resist mask can be used in a plurality of etching steps forprocessing into different patterns. Therefore, a resist maskcorresponding to at least two kinds of different patterns can be formedwith one multi-tone mask. Thus, the number of light-exposure masks canbe reduced and the number of corresponding photolithography steps canalso be reduced, whereby a manufacturing process can be simplified.

Next, the insulating layer 402 a is formed over the conductive layer 401a.

For example, the insulating layer 402 a can be formed by high-densityplasma CVD. For example, high-density plasma CVD is preferably performedusing microwaves (e.g., microwaves with a frequency of 2.45 GHz) inorder to form a dense insulating layer having high withstand voltage andhigh quality. When the oxide semiconductor layer is in contact with thehigh-quality insulating layer formed by high-density plasma CVD, theinterface state can be reduced and good interface characteristics can beobtained.

The insulating layer 402 a can also be formed by another method such assputtering or plasma CVD. Further, heat treatment may be performed afterthe formation of the gate insulating layer 402 a. The heat treatment canimprove the quality of the insulating layer 402 a and the interfacecharacteristics between the insulating layer 402 a and the oxidesemiconductor.

Next, an oxide semiconductor film 530 having a thickness of 2 nm to 200nm inclusive, preferably 5 nm to 30 nm inclusive is formed over theinsulating layer 402 a. For example, the oxide semiconductor film 530can be formed by sputtering.

Note that before the formation of the oxide semiconductor film 530,powdery substances (also referred to as particles or dust) attached on asurface of the insulating layer 402 a are preferably removed by reversesputtering in which an argon gas is introduced and plasma is generated.The reverse sputtering refers to a method in which, without applicationof voltage to a target side, an RF power source is used for applicationof voltage to a substrate side in an argon atmosphere, so that plasma isgenerated to modify a surface of the substrate. Note that instead ofargon, nitrogen, helium, oxygen, or the like may be used.

For example, the oxide semiconductor film 530 can be formed using anoxide semiconductor material which can be used as a material of theoxide semiconductor layer 403 a. In this embodiment, the oxidesemiconductor film 530 is formed by sputtering with use of anIn—Ga—Zn—O-based oxide target. A cross-sectional view at this stagecorresponds to FIG. 9A. Alternatively, the oxide semiconductor film 530can be formed by sputtering in a rare gas (typically, argon) atmosphere,an oxygen atmosphere, or a mixed atmosphere of a rare gas and oxygen.

As a target for forming the oxide semiconductor film 530 by sputtering,for example, an oxide target having a composition ratio ofIn₂O₃:Ga₂O₃:ZnO=1:1:1 [molar ratio] can be used. Without limitation tothe above target, an oxide target having a composition ratio ofIn₂O₃:Ga₂O₃:ZnO=1:1:2 [molar ratio] may be used, for example. Theproportion of the volume of a portion except for an area occupied by aspace and the like with respect to the total volume of the oxide target(also referred to as the filling rate) is 90% to 100% inclusive, andpreferably 95% to 99.9% inclusive. The oxide semiconductor film formedusing a metal oxide target having high filling rate has high density.

Note that as a sputtering gas used for forming the oxide semiconductorfilm 530, for example, a high-purity gas from which an impurity such ashydrogen, water, hydroxyl groups, or hydride is removed is preferablyused.

Before formation of the oxide semiconductor film 530, it is preferablethat the substrate 400 a over which the conductive layer 401 a is formedor the substrate 400 a over which the conductive layer 401 a and theinsulating layer 402 a are formed be preheated in a preheating chamberin the sputtering apparatus, so that an impurity such as hydrogen ormoisture adsorbed on the substrate 400 a is eliminated and removed. Thepreheating can prevent hydrogen, hydroxyl groups, and moisture fromentering the insulating layer 402 a and the oxide semiconductor film530. Note that a cryopump is preferably used as an exhaustion unitprovided in the preheating chamber. The preheating treatment may beomitted. Further, the preheating may be similarly performed beforeformation of the oxide insulating layer 407 a, on the substrate 400 aover which layers up to the conductive layer 405 a and the conductivelayer 406 a have been formed.

When the oxide semiconductor film 530 is formed by sputtering, thesubstrate 400 a is held inside a film formation chamber which is kept ina reduced pressure state, and the substrate temperature is set to 100°C. to 600° C. inclusive, preferably 200° C. to 400° C. inclusive. Byheating the substrate 400 a, the concentration of an impurity containedin the oxide semiconductor film 530 can be reduced. Further, heating ofthe substrate 400 a can reduce damage on the oxide semiconductor film530 due to sputtering. Then, a sputtering gas from which hydrogen andmoisture are removed is introduced while remaining moisture in the filmformation chamber is removed, and the above-described target is used;thus, the oxide semiconductor film 530 is formed over the substrate 400a.

In order to remove remaining moisture in the film formation chamber, anentrapment vacuum pump such as a cryopump, an ion pump, or a titaniumsublimation pump is preferably used. Further, the exhaustion unit may bea turbo pump provided with a cold trap. In the case where the filmformation chamber is exhausted with a cryopump, a hydrogen atom, acompound containing a hydrogen atom (such as water), and furtherpreferably, a compound containing a hydrogen atom and a carbon atom, orthe like is removed. Accordingly, with a cryopump, the concentration ofan impurity contained in the oxide semiconductor film 530 that is formedin the film formation chamber can be reduced.

As one example of the film formation conditions, the following can beemployed: the distance between the substrate 400 and the target is 100mm, the pressure is 0.6 Pa, the direct-current (DC) power is 0.5 kW, andthe atmosphere is an oxygen atmosphere (the proportion of oxygen flow is100%). Note that a pulsed direct-current power supply is preferably usedbecause powdery substances generated at the time of film formation canbe reduced and the film thickness can be made uniform.

Next, a second photolithography process is carried out: a second resistmask is formed over the oxide semiconductor film 530, the oxidesemiconductor film 530 is selectively etched with use of the secondresist mask to process the oxide semiconductor film 530 into anisland-shaped oxide semiconductor layer, and the second resist mask isremoved.

In the case of forming a contact hole in the insulating layer 402 a, thecontact hole can be formed at the time of processing the oxidesemiconductor film 530 into the island-shaped oxide semiconductor layer.

For example, dry etching, wet etching, or both dry etching and wetetching can be employed for etching the oxide semiconductor film 530. Asan etchant used for wet etching of the oxide semiconductor film 530, amixed solution of phosphoric acid, acetic acid, and nitric acid can beused, for example. Further, ITO07N (produced by KANTO CHEMICAL CO.,INC.) may also be used.

Next, the oxide semiconductor layer is subjected to first heattreatment. Through the first heat treatment, the oxide semiconductorlayer can be dehydrated or dehydrogenated. The temperature of the firstheat treatment is 400° C. to 750° C. inclusive, or equal to or higherthan 400° C. and lower than the strain point of the substrate. Here, thesubstrate is put in an electric furnace that is a kind of heat treatmentapparatus and heat treatment is performed on the oxide semiconductorlayer in a nitrogen atmosphere at 450° C. for one hour, and then theoxide semiconductor layer is not exposed to the air so that entry ofwater and hydrogen into the oxide semiconductor layer is prevented. Inthis manner, the oxide semiconductor layer 403 a is obtained (see FIG.9B).

The heat treatment apparatus is not limited to the electric furnace andmay be the one provided with a device for heating a process object usingheat conduction or heat radiation from a heating element such as aresistance heating element. For example, an RTA (rapid thermalannealing) apparatus such as a GRTA (gas rapid thermal annealing)apparatus or an LRTA (lamp rapid thermal annealing) apparatus can beused. An LRTA apparatus is an apparatus for heating a process object byradiation of light (an electromagnetic wave) emitted from a lamp such asa halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arclamp, a high-pressure sodium lamp, or a high-pressure mercury lamp. AGRTA apparatus is an apparatus for heat treatment using ahigh-temperature gas. As the high-temperature gas, an inert gas whichdoes not react with a process object by heat treatment, such as nitrogenor a rare gas like argon, is used.

For example, as the first heat treatment, GRTA may be performed in thefollowing manner. The substrate is transferred to an inert gas which hasbeen heated to a high temperature of 650° C. to 700° C., heated forseveral minutes, and transferred from the heated inert gas.

Note that in the first heat treatment, it is preferable that water,hydrogen, and the like be not contained in nitrogen or a rare gas suchas helium, neon, or argon. It is also preferable that nitrogen or a raregas such as helium, neon, or argon introduced into the heat treatmentapparatus have a purity of 6N (99.9999%) or more, preferably, 7N(99.99999%) or more (that is, the impurity concentration is set to beequal to or lower than 1 ppm, preferably, equal to or lower than 0.1ppm).

After the oxide semiconductor layer is heated by the first heattreatment, a high-purity oxygen gas, a high-purity N₂O gas, or ultra-dryair (having a dew point of −40° C. or lower, preferably −60° C. orlower) may be introduced into the same furnace. It is preferable thatthe oxygen gas or the N₂O gas do not contain water, hydrogen, and thelike. The purity of the oxygen gas or the N₂O gas which is introducedinto the heat treatment apparatus is preferably equal to or more than6N, more preferably equal to or more than 7N (i.e., the impurityconcentration of the oxygen gas or the N₂O gas is preferably equal to orlower than 1 ppm, more preferably equal to or lower than 0.1 ppm). Bythe effect of the oxygen gas or the N₂O gas, oxygen that has beenreduced through the step of eliminating an impurity by the dehydrationor dehydrogenation treatment is supplied; thus, the oxide semiconductorlayer 403 a is highly purified.

The first heat treatment may also be performed on the oxidesemiconductor film 530 that has not been processed into theisland-shaped oxide semiconductor layer. In such a case, the substrateis taken out of the heating apparatus after the first heat treatment andthen the oxide semiconductor film 530 is processed into theisland-shaped oxide semiconductor layer.

Other than the above-described timings, the first heat treatment may beperformed after the formation of the oxide semiconductor layer, forexample, after formation of the conductive layer 405 a and theconductive layer 406 a over the oxide semiconductor layer 403 a or afterformation of the oxide insulating layer 407 a over the conductive layer405 a and the conductive layer 406 a.

In the case of forming a contact hole in the insulating layer 402 a, thecontact hole may be formed before the first heat treatment is performed.

The oxide semiconductor layer may be formed using an oxide semiconductorfilm which is formed through two deposition steps so as to be a thickfilm including a crystalline region (a single crystal region), that is,a crystalline region having a c-axis aligned in a directionperpendicular to a surface of the film, regardless of the material of abase component such as an oxide, a nitride, or a metal. For example, afirst oxide semiconductor film with a thickness of 3 nm to 15 nminclusive is deposited and subjected to first heat treatment at atemperature of 450° C. to 850° C. inclusive, preferably 550° C. to 750°C. inclusive under an atmosphere of nitrogen, oxygen, a rare gas, or dryair, so that the first oxide semiconductor film which includes acrystalline region (including a plate-like crystal) in a regionincluding a surface is formed. Then, a second oxide semiconductor filmthat is thicker than the first oxide semiconductor film is formed andsubjected to second heat treatment at a temperature of 450° C. to 850°C. inclusive, preferably 600° C. to 700° C. inclusive, so that crystalgrowth proceeds toward the upper side from the first oxide semiconductorfilm to the second oxide semiconductor film using the first oxidesemiconductor film as a seed of the crystal growth, and the entireregion of the second oxide semiconductor film is crystallized. Using thefilm including a crystalline region, which is thick as a consequence, anoxide semiconductor layer may be formed.

Next, a second conductive film is formed over the insulating layer 402 aand the oxide semiconductor layer 403 a.

As the second conductive film, a film of a metal material such asaluminum, chromium, copper, tantalum, titanium, molybdenum, or tungsten,or an alloy material which contains any of the metal materials as a maincomponent can be used, for example. The second conductive film can alsobe formed by stacking films of materials which can be applied to thesecond conductive film.

Next, a third photolithography process is carried out: a third resistmask is formed over the second conductive film, the second conductivefilm is selectively etched with use of the third resist mask to form theconductive layer 405 a and the conductive layer 406 a, and the thirdresist mask is removed (see FIG. 9C).

Note that another wiring may be formed using the second conductive filmat the time of forming the conductive layer 405 a and the conductivelayer 406 a.

In light exposure in forming the third resist mask, ultraviolet light,KrF laser light, or ArF laser light is preferably used. A channel lengthL of the transistor to be completed later depends on the width of aninterval between a bottom end of the conductive layer 405 a and a bottomend of the conductive layer 406 a which are adjacent to each other overthe oxide semiconductor layer 403 a. In the case where the channellength L is less than 25 nm, the light exposure at the time of formingthe third resist mask is preferably performed using extreme ultravioletlight having an extremely short wavelength of several nanometers toseveral tens of nanometers. In light exposure using extreme ultravioletlight, resolution is high and depth of focus is large. Therefore, thechannel length L of the transistor to be completed later can be made 10nm to 1000 nm inclusive, and the use of the transistor formed throughsuch light exposure enables higher speed operation of a circuit. Inaddition, the off-current of the transistor is extremely low, whichresults in a reduction in power consumption.

In the case of etching the second conductive film, etching conditionsare preferably optimized in order to prevent the oxide semiconductorlayer 403 a from being divided by the etching. However, it is difficultto set the conditions under which only the second conductive film can beetched and the oxide semiconductor layer 403 a is not etched at all. Insome cases, part of the oxide semiconductor layer 403 a is etched at thetime of etching the second conductive film, whereby the oxidesemiconductor layer 403 a comes to include a groove portion (depressionportion).

In this embodiment, a titanium film is used as an example of the secondconductive film, an In—Ga—Zn—O-based oxide semiconductor is used as anexample of the oxide semiconductor layer 403 a, and an ammonia hydrogenperoxide solution (a mixture of ammonia, water, and a hydrogen peroxidesolution) is used as an etchant.

Next, the oxide insulating layer 407 a is formed over the oxidesemiconductor layer 403 a, the conductive layer 405 a, and theconductive layer 406 a. At this time, the oxide insulating layer 407 ais in contact with part of the top surface of the oxide semiconductorlayer 403 a.

The oxide insulating layer 407 a can be formed to a thickness of atleast 1 nm or more using a method by which impurities such as water orhydrogen are not introduced into the oxide insulating layer 407 a, suchas a sputtering method, as appropriate. When hydrogen is contained inthe oxide insulating layer 407 a, entry of the hydrogen to the oxidesemiconductor layer, or extraction of oxygen in the oxide semiconductorlayer by the hydrogen is caused, thereby causing the backchannel of theoxide semiconductor layer to have lower resistance (to have an n-typeconductivity), so that a parasitic channel may be formed. Therefore, inorder to form the oxide insulating layer 407 a containing as littlehydrogen as possible, it is important to employ a formation method inwhich hydrogen is not used.

In this embodiment, as the oxide insulating layer 407 a, a silicon oxidefilm having a thickness of 200 nm is formed by sputtering. The substratetemperature at the time of the film formation may be room temperature to300° C. inclusive; in this embodiment, 100° C. as an example. Theformation of a silicon oxide film by sputtering can be performed in arare gas (typically, argon) atmosphere, an oxygen atmosphere, or a mixedatmosphere of a rare gas and oxygen.

Further, a silicon oxide target or a silicon target can be used as atarget for forming the oxide insulating layer 407 a. For example, withuse of a silicon target, a silicon oxide film can be formed bysputtering under an atmosphere containing oxygen.

In order to remove remaining moisture in a film formation chamber thatis used for forming the oxide insulating layer 407 a, an entrapmentvacuum pump (such as a cryopump) is preferably used, for example. Byremoving remaining moisture in a film formation chamber with a cryopump,the concentration of an impurity contained in the oxide insulating layer407 a can be reduced. As an exhaustion unit for removing remainingmoisture in the film formation chamber that is used for forming theoxide insulating layer 407 a, for example, a turbo pump provided with acold trap can be used.

As a sputtering gas used for forming the oxide semiconductor film 407 a,for example, a high-purity gas from which an impurity such as hydrogen,water, hydroxyl groups, or hydride is removed is preferably used.

Before formation of the oxide insulating layer 407 a, plasma treatmentwith the use of a gas such as N₂O, N₂, or Ar may be performed to removewater or the like adsorbed on an exposed surface of the oxidesemiconductor layer 403 a. In the case where plasma treatment isperformed, the oxide insulating layer 407 a which is in contact withpart of the upper surface of the oxide semiconductor layer 403 a ispreferably formed without exposure to the air.

Then, second heat treatment (preferably, at a temperature of 200° C. to400° C. inclusive, for example, 250° C. to 350° C. inclusive) can beperformed in an inert gas atmosphere or in an oxygen gas atmosphere. Forexample, the second heat treatment is performed at 250° C. in a nitrogenatmosphere for one hour. Through the second heat treatment, heat isapplied while part of the upper surface of the oxide semiconductor layer403 a is in contact with the oxide insulating layer 407 a.

Through the above-described process, the first heat treatment isperformed on the oxide semiconductor film, so that an impurity such ashydrogen, moisture, hydroxyl groups, or hydride (also referred to as ahydrogen compound) can be intentionally removed from the oxidesemiconductor layer, and in addition, oxygen can be supplied to theoxide semiconductor layer. Therefore, the oxide semiconductor layer ishighly purified.

Through the above process, the transistor is completed (see FIG. 9D).

When a silicon oxide layer having many defects is used as the oxideinsulating layer 407 a, the heat treatment after formation of thesilicon oxide layer has an effect of diffusing an impurity such ashydrogen, moisture, hydroxyl groups, or hydride contained in the oxidesemiconductor layer 403 a to the oxide insulating layer 407 a, so thatthe impurity contained in the oxide semiconductor layer 403 a can befurther reduced.

The protective insulating layer 409 a may be further formed over theoxide insulating layer 407 a. For example, a silicon nitride film isformed by RF sputtering. The RF sputtering is preferably used as aformation method of the protective insulating layer 409 a because itachieves high mass productivity. In this embodiment, as the protectiveinsulating layer 409 a, a silicon nitride film is formed as an example(see FIG. 9E).

In this embodiment, the protective insulating layer 409 a is formed insuch a manner that the substrate 400 a over which layers up to the oxideinsulating layer 407 a are formed is heated at a temperature of 100° C.to 400° C., a sputtering gas containing high-purity nitrogen from whichhydrogen and moisture are removed is introduced, and a silicon nitridefilm is formed with use of a target of a silicon semiconductor. In thatcase also, the protective insulating layer 409 a is preferably formedwhile removing remaining moisture in a treatment chamber, similarly tothe case of forming the oxide insulating layer 407 a.

After formation of the protective insulating layer 409 a, heat treatmentmay be further performed at a temperature of 100° C. to 200° C.inclusive under the air for 1 hour to 30 hours inclusive. The heattreatment may be performed at a fixed heating temperature.Alternatively, the following change in heating temperature may beconducted plural times repeatedly: an increase from room temperature toa temperature of 100° C. to 200° C. inclusive and then a decrease toroom temperature. That is an example of the method for manufacturing thetransistor illustrated in FIG. 8A.

As described above, the transistor shown in this embodiment is atransistor including an oxide semiconductor layer as a channel formationlayer. The oxide semiconductor layer used in the transistor is highlypurified by heat treatment and thereby becomes an i-type orsubstantially i-type oxide semiconductor layer. Such a transistor can beused as a transistor having a high withstand voltage that is used in thesemiconductor devices shown in the above embodiments.

The highly-purified oxide semiconductor layer includes extremely fewcarriers (close to 0). The carrier concentration of the oxidesemiconductor layer is less than 1×10¹⁴/cm³, preferably less than1×10¹²/cm³, and more preferably less than 1×10¹¹/cm³. Since the numberof carriers in the oxide semiconductor layer is extremely small, theoff-current of the transistor of this embodiment in reverse bias can bereduced. It is preferable that the off-current be as low as possible. Inthe transistor of this embodiment, the off-current per micrometer ofchannel width can be made equal to or less than 10 aA/μm (1×10⁻¹⁷ A/μm),equal to or less than 1 aA/μm (1×10⁻¹⁸ A/μm), equal to or less than 10zA/μm (1×10⁻²⁰ A/μm), and further equal to or less than 1 zA/μm (1×10⁻²¹A/μm).

The transistor of this embodiment has a relatively high field-effectmobility and is capable of high-speed driving. Therefore, when thetransistor of this embodiment is used, for example, the voltage input tothe semiconductor device can be controlled more quickly.

Note that this embodiment can be combined with or replaced by any of theother embodiments, as appropriate.

Embodiment 7

In this embodiment, an example of a plurality of transistors that can beapplied to any of the semiconductor devices shown in the aboveembodiments will be described.

An example of a structure of a plurality of transistors in thisembodiment which can be applied to any of the semiconductor devicesshown in the above embodiments will be described with reference to FIGS.10A and 10B. FIGS. 10A and 10B are cross-sectional schematic diagramseach illustrating an example of the structure of the plurality oftransistors in this embodiment.

The structure illustrated in FIG. 10A includes a transistor 601 a and atransistor 602 a.

The transistor 601 a is provided over a substrate 600 with an insulatinglayer 603, an insulating layer 604, and an insulating layer 605interposed therebetween.

Further, the transistor 601 a includes a semiconductor layer 611 servingas a channel formation layer, an insulating layer 617 a serving as agate insulating layer, a conductive layer 618 a serving as a gateelectrode, and an insulating layer 619 a and an insulating layer 620 aeach serving as a sidewall insulating layer.

The semiconductor layer 611 is provided over the substrate 600 with theinsulating layer 603, the insulating layer 604, and the insulating layer605 interposed therebetween, the insulating layer 617 a is provided overthe semiconductor layer 611, the conductive layer 618 a is provided overthe semiconductor layer 611 with the insulating layer 617 a interposedtherebetween, and the insulating layer 619 a and the insulating layer620 a are provided in contact with side surfaces of the conductive layer618 a.

Furthermore, the semiconductor layer 611 includes a channel formationregion 612 under the conductive layer 618 a, an impurity region 613 aand an impurity region 614 a serving as a source or drain region, ahigh-resistance impurity region 615 a between the channel formationregion 612 and the impurity region 613 a, and a high-resistance impurityregion 616 a between the channel formation region 612 and the impurityregion 614 a.

The transistor 602 a is provided over a top surface of the transistor601 a with an insulating layer 621 a, an insulating layer 622 a servingas a planarization layer, and an insulating layer 623 a interposedtherebetween. As the transistor 602 a, for example, any of thetransistors shown in the above Embodiment 6 can be used. As an exampleof the transistor 602 a, FIG. 10A illustrates the transistor having thestructure illustrated in FIG. 8A.

A conductive layer 626 a serving as one of a source electrode and adrain electrode of the transistor 602 a is in contact with the impurityregion 614 a through an opening formed in the insulating layer 621 a,the insulating layer 622 a, and the insulating layer 623 a. Note thatthe conductive layer 626 a may be in contact with the impurity region614 a via a plurality of conductive layers.

A conductive layer 625 a which is formed on the same layer as theconductive layer 626 a serving as one of the source electrode and thedrain electrode of the transistor 602 a is in contact with the impurityregion 613 a through an opening formed in the insulating layer 621 a,the insulating layer 622 a, and the insulating layer 623 a. Note thatthe conductive layer 625 a may be in contact with the impurity region613 a via a plurality of conductive layers.

Further, in the transistor 602 a, an oxide insulating layer 627 a is incontact with part of a top surface of an oxide semiconductor layerserving as a channel formation layer (part of the oxide semiconductorlayer over which conductive layers serving as a source or drainelectrode are not provided). A protective insulating layer 628 a isprovided over the oxide insulating layer 627 a.

The structure illustrated in FIG. 10B includes a transistor 601 b and atransistor 602 b.

The transistor 601 b includes a semiconductor substrate 610 having achannel formation region, an insulating layer 617 b serving as a gateinsulating layer, a conductive layer 618 b serving as a gate electrode,and an insulating layer 619 b, an insulating layer 620 b, an insulatinglayer 608, and an insulating layer 609 serving as sidewall insulatinglayers.

The insulating layer 617 b is provided over the semiconductor substrate610, and the conductive layer 618 b is provided over the semiconductorsubstrate 610 with the insulating layer 617 b interposed therebetween.

Further, the semiconductor substrate 610 includes an insulating layer606 serving as an isolation insulating layer with the other elementsprovided in the semiconductor substrate 610, an impurity region 613 band an impurity region 614 b serving as a source or drain region, ahigh-resistance impurity region 615 b between the channel formationregion and the impurity region 613 b, and a high-resistance impurityregion 616 b between the channel formation region and the impurityregion 614 b.

The transistor 602 b is provided over a top surface of the transistor601 b with an insulating layer 621 b, an insulating layer 622 b, and aninsulating layer 623 b interposed therebetween. As the transistor 602 b,for example, any of the transistors shown in the above Embodiment 6 canbe used. As an example of the transistor 602 b, FIG. 10B illustrates thetransistor having the structure illustrated in FIG. 8A.

A conductive layer 626 b serving as one of the source electrode and thedrain electrode of the transistor 602 b is in contact with the impurityregion 614 b through an opening formed in the insulating layer 621 b,the insulating layer 622 b, and the insulating layer 623 b. Note thatthe conductive layer 626 b may be in contact with the impurity region614 b via a plurality of conductive layers.

A conductive layer 625 b which is provided on the same layer as theconductive layer 626 b serving as one of the source electrode and thedrain electrode of the transistor 602 b is in contact with the impurityregion 613 b through an opening formed in the insulating layer 621 b,the insulating layer 622 b, and the insulating layer 623 b. Note thatthe conductive layer 625 b may be in contact with the impurity region613 b via a plurality of conductive layers.

Further, in the transistor 602 b, an oxide insulating layer 627 b is incontact with part of a top surface of an oxide semiconductor layerserving as a channel formation layer (part of the oxide semiconductorlayer over which conductive layers serving as a source or drainelectrode are not provided). A protective insulating layer 628 b isprovided over the oxide insulating layer 627 b.

As the substrate 600, for example, a glass substrate, a ceramicsubstrate, a quartz substrate, a plastic substrate, or a siliconsubstrate can be used.

As the semiconductor substrate 610, for example, a silicon substrate, agermanium substrate, or a silicon germanium substrate can be used. Thesemiconductor substrate 610 may contain an impurity element impartingp-type conductivity.

As the insulating layer 603, the insulating layer 604, and theinsulating layer 606, a silicon nitride layer, a silicon oxide layer, asilicon nitride oxide layer, a silicon oxynitride layer, an aluminumoxide layer, or an aluminum oxynitride layer can be used, for example.

As the insulating layer 605, it is possible to use, for example, asilicon oxide layer containing hydrogen, a silicon nitride layercontaining hydrogen, a silicon nitride layer containing oxygen andhydrogen, a silicon oxynitride layer, or a silicon nitride oxide layer.For example, silicon oxide formed using organosilane is preferably usedas silicon oxide containing hydrogen. This is because the silicon oxidefilm formed using organosilane can increase the bonding strength betweenthe substrate 600 and the semiconductor layer 611. As organosilane, itis possible to use, for example, a silicon-containing compound such astetraethoxysilane (TEOS, Si(OC₂H₅)₄), tetramethylsilane (TMS, Si(CH₃)₄),tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane(OMCTS), hexamethyldisilazane (HMDS), triethoxysilane (SiH(OC₂H₅)₃), ortris(dimethylamino)silane (SiH(N(CH₃)₂)₃).

As the semiconductor layer 611, a layer containing one or both ofsilicon and germanium can be used, for example. Further, as thesemiconductor layer 611, a single crystal semiconductor layer, apolycrystalline semiconductor layer, a microcrystalline semiconductorlayer, or an amorphous semiconductor layer can be used.

For example, in the case where a single crystal semiconductor layer isused as the semiconductor layer 611, first, a single crystalsemiconductor substrate is prepared and a damaged region is formed inthe single crystal semiconductor substrate by, for example, ionirradiation. After the single crystal semiconductor substrate includingthe damaged region is bonded to the substrate 600 with the insulatinglayers 603 to 605 interposed therebetween, part of the single crystalsemiconductor substrate is separated from the bonded substrate (thesingle crystal semiconductor substrate and the substrate 600) with thedamaged region used as a cleavage surface. Then, the remaining singlecrystal semiconductor region on the substrate 600 is selectively removedby etching or the like, whereby the single crystal semiconductor layercan be formed.

The impurity region 613 a, the impurity region 613 b, the impurityregion 614 a, and the impurity region 614 b are regions containing animpurity element which imparts n-type or p-type conductivity, and formedby, for example, addition of an impurity element which imparts n-type orp-type conductivity.

The high-resistance impurity region 615 a, the high-resistance impurityregion 615 b, the high-resistance impurity region 616 a, and thehigh-resistance impurity region 616 b are regions having a higherresistance than the impurity region 613 a, the impurity region 613 b,the impurity region 614 a, and the impurity region 614 b, and are formedby, for example, addition of an impurity element imparting n-type orp-type conductivity at a lower concentration than that of the impurityregion 613 a, the impurity region 613 b, the impurity region 614 a, andthe impurity region 614 b.

As the insulating layers 617 a and 617 b, a silicon oxide layer, asilicon nitride layer, a silicon oxynitride layer, a silicon nitrideoxide layer, an aluminum oxide layer, an aluminum nitride layer, analuminum oxynitride layer, an aluminum nitride oxide layer, or a hafniumoxide layer can be used, for example. The insulating layers 617 a and617 b can also be formed by stacking layers of materials which can beapplied to the insulating layers 617 a and 617 b. The layers ofmaterials which can be applied to the insulating layers 617 a and 617 bcan be formed by plasma CVD, sputtering, or the like. For example, theinsulating layers 617 a and 617 b can be formed in such a manner that asilicon nitride layer is formed by plasma CVD and a silicon oxide layeris formed over the silicon nitride layer by plasma CVD.

As the conductive layers 618 a and 618 b, a layer of a metal materialsuch as molybdenum, titanium, chromium, tantalum, tungsten, aluminum,copper, neodymium, or scandium, or an alloy material which contains anyof the metal materials as a main component can be used. The conductivelayers 618 a and 618 b can also be formed by stacking layers ofmaterials which can be applied to the conductive layers 618 a and 618 b.For example, the conductive layers 618 a and 618 b can be formed in sucha manner that a conductive film is formed by sputtering and then theconductive film is selectively etched.

As the insulating layer 619 a, the insulating layer 619 b, theinsulating layer 608, and the insulating layer 609, a silicon nitridelayer, a silicon oxide layer, a silicon nitride oxide layer, a siliconoxynitride layer, an aluminum oxide layer, or an aluminum oxynitridelayer can be used, for example.

As the insulating layer 621 a and the insulating layer 621 b, a siliconnitride layer, a silicon oxide layer, a silicon nitride oxide layer, asilicon oxynitride layer, an aluminum oxide layer, or an aluminumoxynitride layer can be used, for example. The insulating layer 621 aand the insulating layer 621 b can also be formed by stacking layers ofmaterials which can be applied to the insulating layer 621 a and theinsulating layer 621 b. The insulating layer 621 a and the insulatinglayer 621 b are formed by plasma CVD or the like.

As the insulating layer 622 a and the insulating layer 622 b, an organicmaterial layer or an inorganic material layer can be used, for example.The insulating layer 622 a and the insulating layer 622 b can also beformed by stacking layers of materials which can be applied to theinsulating layer 622 a and the insulating layer 622 b. The insulatinglayer 622 a and the insulating layer 622 b are formed by plasma CVD orthe like.

As the insulating layer 623 a and the insulating layer 623 b, a siliconnitride layer, a silicon oxide layer, a silicon nitride oxide layer, asilicon oxynitride layer, an aluminum oxide layer, or an aluminumoxynitride layer can be used, for example. The insulating layer 623 aand the insulating layer 623 b can also be formed by stacking layers ofmaterials which can be applied to the insulating layer 623 a and theinsulating layer 623 b. The insulating layer 623 a and the insulatinglayer 623 b are formed by plasma CVD or the like.

As the conductive layer 625 a, the conductive layer 625 b, theconductive layer 626 a, and the conductive layer 626 b, a layer of amaterial which can be applied to a conductive layer serving as thesource or drain electrode of the transistor 602 a and the transistor 602b can be used, for example. The conductive layer 625 a, the conductivelayer 625 b, the conductive layer 626 a, and the conductive layer 626 bcan also be formed by stacking layers of materials which can be appliedto the conductive layer 625 a, the conductive layer 625 b, theconductive layer 626 a, and the conductive layer 626 b.

As illustrated in the example of FIGS. 10A and 10B, the semiconductordevices in the above embodiments can be formed by using a plurality oftransistors having different structures. Consequently, a transistor withan optimal structure can be selectively used in accordance with theproperty of each circuit; for example, an n-channel transistor and ap-channel transistor can be selectively manufactured.

Note that this embodiment can be combined with or replaced by any of theother embodiments, as appropriate.

Embodiment 8

In this embodiment, description will be made on an electronic deviceincluding the semiconductor device which is shown in the aboveembodiments and is capable of generating a power supply voltage throughwireless communication.

Examples of a configuration of the electronic device in this embodimentwill be described with reference to FIGS. 11A to 11F. FIGS. 11A to 11Fare views each illustrating an example of the configuration of theelectronic device in this embodiment.

The electronic device illustrated in FIG. 11A is a personal digitalassistant. The personal digital assistant illustrated in FIG. 11Aincludes at least a display portion 1001 and a chip 1003. The personaldigital assistant illustrated in FIG. 11A can be combined with a touchpanel or the like, and can be used as an alternative to a variety ofportable objects. For example, when the display portion 1001 is providedwith an operation portion 1002 using a touch panel, the personal digitalassistant can be used as a cellular phone. As the touch panel, forexample, a resistive touch panel, an infrared touch panel, a capacitivetouch panel, or an optical touch panel can be used. Note that theoperation portion 1002 is not necessarily provided in the displayportion 1001, and operation buttons may be provided separately in thepersonal digital assistant illustrated in FIG. 11A. Moreover, since thechip 1003 is provided, the personal digital assistant illustrated inFIG. 11A can generate a power supply voltage through wirelesscommunication and operate with the generated power supply voltage. Thepersonal digital assistant is sometimes used in the environment wherepower cannot be supplied externally; therefore, the semiconductor deviceof one embodiment of the present invention, which is capable ofgenerating a power supply voltage through wireless communication, ispreferably used for the personal digital assistant.

The electronic device illustrated in FIG. 11B is an information guideterminal including an automotive navigation system, for example. Theinformation guide terminal illustrated in FIG. 11B includes at least adisplay portion 1101 and a chip 1104, and can also have operationbuttons 1102, an external input terminal 1103, and the like. The in-cartemperature changes greatly in accordance with the outside-airtemperature, and sometimes exceeds 50° C. Since the characteristics ofthe semiconductor device shown in the above embodiments hardly changedue to the temperature, the semiconductor device in the aboveembodiments is particularly effective under the circumstances where thetemperature greatly changes, such as the inside of a car. Moreover,since the chip 1104 is provided, the information guide terminalillustrated in FIG. 11B can generate a power supply voltage throughwireless communication and operate with the generated power supplyvoltage. The information guide terminal is sometimes used in theenvironment where power cannot be supplied externally; therefore, thesemiconductor device of one embodiment of the present invention, whichis capable of generating a power supply voltage through wirelesscommunication, is preferably used for the information guide terminal.

The electronic device illustrated in FIG. 11C is a laptop personalcomputer. The laptop personal computer illustrated in FIG. 11C includesa housing 1201, a display portion 1202, a speaker 1203, an LED lamp1204, a pointing device 1205, a connection terminal 1206, a keyboard1207, and a chip 1208. Since the chip 1208 is provided, the electronicdevice illustrated in FIG. 11C can generate a power supply voltagethrough wireless communication and operate with the generated powersupply voltage. The laptop personal computer is sometimes used in theenvironment where power cannot be supplied externally; therefore, thesemiconductor device of one embodiment of the present invention, whichis capable of generating a power supply voltage through wirelesscommunication, is preferably used for the laptop personal computer.

The electronic device illustrated in FIG. 11D is a portable gamemachine. The portable game machine illustrated in FIG. 11D includes adisplay portion 1301, a display portion 1302, a speaker 1303, aconnection terminal 1304, an LED lamp 1305, a microphone 1306, arecording medium reading portion 1307, operation buttons 1308, a sensor1309, and a chip 1310. Since the chip 1310 is provided, the portablegame machine illustrated in FIG. 11D can generate a power supply voltagethrough wireless communication and operate with the generated powersupply voltage. The portable game machine is sometimes used in theenvironment where power cannot be supplied externally; therefore, thesemiconductor device of one embodiment of the present invention, whichis capable of generating a power supply voltage through wirelesscommunication, is preferably used for the portable game machine.

The electronic device illustrated in FIG. 11E is an e-book reader. Thee-book reader illustrated in FIG. 11E includes at least a housing 1401,a housing 1403, a display portion 1405, a display portion 1407, a hinge1411, and a chip 1426.

The housing 1401 and the housing 1403 are connected with the hinge 1411.The e-book reader illustrated in FIG. 11E can be opened and closed withthe hinge 1411 as an axis. With such a structure, the e-book reader canbe handled like a paper book. The display portion 1405 is incorporatedin the housing 1401 and the display portion 1407 is incorporated in thehousing 1403. The display portion 1405 and the display portion 1407 maydisplay different images. For example, one image can be displayed acrossboth the display portions. With the structure where different images aredisplayed on the display portion 1405 and the display portion 1407, forexample, text can be displayed on a display portion on the right side(the display portion 1405 in FIG. 11E) and graphics can be displayed ona display portion on the left side (the display portion 1407 in FIG.11E).

In the e-book reader illustrated in FIG. 11E, an operation portion orthe like can be provided in the housing 1401. For example, the e-bookreader illustrated in FIG. 11E may include a power switch 1421,operation keys 1423, and a speaker 1425. In the case where an image witha plurality of pages is displayed in the e-book reader illustrated inFIG. 11E, the pages can be turned with the operation keys 1423.Furthermore, in the e-book reader illustrated in FIG. 11E, a keyboard ora pointing device may be provided in the display portion 1405 and thedisplay portion 1407, or in the display portion 1405 or the displayportion 1407. Also in the e-book reader illustrated in FIG. 11E, anexternal connection terminal (an earphone terminal, a USB terminal, aterminal connectable to a variety of cables such as an AC adapter and aUSB cable, or the like), a recording medium insertion portion, and thelike may be provided on the back surface or side surface of the housing1401 and the housing 1403. In addition, the e-book reader illustrated inFIG. 11E may have a function of an electronic dictionary.

Since the chip 1426 is provided, the e-book reader illustrated in FIG.11E can generate a power supply voltage through wireless communicationand operate with the generated power supply voltage. The e-book readeris sometimes used in the environment where power cannot be suppliedexternally; therefore, the semiconductor device of one embodiment of thepresent invention, which is capable of generating a power supply voltagethrough wireless communication, is preferably used for the e-bookreader.

The e-book reader illustrated in FIG. 11E can have a configurationcapable of transmitting and receiving data through wirelesscommunication. With such a configuration, desired book data or the likecan be purchased and downloaded from an electronic book server.

The electronic device illustrated in FIG. 11F is a display. The displayillustrated in FIG. 11F includes a housing 1501, a display portion 1502,a speaker 1503, an LED lamp 1504, operation buttons 1505, a connectionterminal 1506, a sensor 1507, a microphone 1508, a support base 1509,and a chip 1510. Since the chip 1510 is provided, the displayillustrated in FIG. 11F can generate a power supply voltage throughwireless communication and operate with the generated power supplyvoltage. When the semiconductor device of one embodiment of the presentinvention, which is capable of generating a power supply voltage throughwireless communication, is used for the display, a power supply terminalor the like does not need to be provided, resulting in a reduction inthe number of wirings and terminals.

Note that as the chip 1003, the chip 1104, the chip 1208, the chip 1310,the chip 1426, or the chip 1510, the semiconductor device shown in theabove embodiments, which is capable of generating a power supply voltagethrough wireless communication, can be used.

As illustrated in the examples of FIGS. 11A to 11F, the electronicdevices in this embodiment can generate a power supply voltage throughwireless communication. With such a configuration, the electronicdevices can be used for a certain period even in the environment wherethe electronic devices cannot be connected to a power feeding means.

Note that the electronic devices shown in this embodiment can have apower storage device in which a generated power supply voltage isstored. Consequently, the electronic devices can be used for a certainperiod even without an external power supply, resulting in animprovement in convenience. As the power storage device, for example,one or more of a lithium ion secondary battery, a lithium ion capacitor,an electric double-layer capacitor, and a redox capacitor can be used.For example, a lithium ion secondary battery and a lithium ion capacitorcan be used together, whereby a power storage device which can charge ordischarge at high speed and can supply electric power for a long timecan be formed. Note that the power storage device is not limited to thelithium ion secondary battery. As the power storage device, a secondarybattery in which another alkali metal ion, alkaline earth metal ion, orthe like is used as a mobile ion may be used. Further, the power storagedevice is not limited to the lithium ion capacitor. As the power storagedevice, a capacitor in which another alkali metal ion, alkaline earthmetal ion, or the like is used as a mobile ion may be used.

The application of the semiconductor device in the above embodiments isnot limited to the electronic devices illustrated in FIGS. 11A to 11F,and for example, the semiconductor device can also be applied to anelectric car.

Note that this embodiment can be combined with or replaced by any of theother embodiments, as appropriate.

Embodiment 9

In this embodiment description will be made on an information mediumincluding the semiconductor device which is shown in the aboveembodiments and is capable of transmitting and receiving signals throughwireless communication.

Examples of a configuration of the information medium in this embodimentwill be described with reference to FIGS. 12A to 12D. FIGS. 12A to 12Dare views each illustrating an example of the configuration of theinformation medium in this embodiment.

The information medium illustrated in FIG. 12A is a card certificaterecording personal data. The card certificate illustrated in FIG. 12Aincludes a chip 800, so that security function such as prevention offorgery can be improved. As the card certificate, for example, driver'slicenses, resident cards, or passports can be given. With highreliability, the chip 800 is suitable for the card certificate and thelike which are used for a long period.

The information medium illustrated in FIG. 12B is a ticket informationmedium. The ticket information medium illustrated in FIG. 12B includes achip 801, so that information other than that printed on the ticketinformation medium can be stored in the chip 801. In addition, the chip801 can improve security function such as prevention of forgery of theticket information medium illustrated in FIG. 12B. Since the chip 801has high reliability, for example, a cutoff portion is provided in partof the ticket and only the chip 801 is cut along the cutoff portion whenthe ticket information medium is no longer used, whereby only the chip801 can be collected and reused. As the ticket information medium, forexample, paper money, railway tickets, securities, or other tickets canbe given.

The information medium illustrated in FIG. 12C is a coin informationmedium. The coin information medium includes a chip 802, so thatinformation other than that printed on the coin information medium canbe stored in the chip 802. In addition, the chip 802 can improvesecurity function such as prevention of forgery of the coin informationmedium illustrated in FIG. 12C. As the coin information medium, forexample, coins, railway tickets, securities, or other tickets can begiven.

The information medium illustrated in FIG. 12D is an article. Thearticle includes a chip 803, so that information other than that printedon the article can be stored in the chip 803. In addition, the chip 803can improve security function such as prevention of forgery of thearticle illustrated in FIG. 12D. There is no particular limitation onthe article, and for example, various articles such as electronicappliances and household commodities can be given.

As the chips 800 to 803, for example, the semiconductor device shown inthe above embodiments, which is capable of wireless communication, canbe employed.

As described above, the information medium in this embodiment includes achip capable of wireless communication. With such a configuration, thespecific data of the information medium including a chip can be readthrough wireless communication and utilized. As a result, theinformation medium can be managed more easily with higher security.

Note that this embodiment can be combined with or replaced by any of theother embodiments, as appropriate.

Example 1

In this example, an example of the semiconductor device shown in theabove embodiments will be described.

Semiconductor devices shown in this example are a semiconductor devicehaving the configuration illustrated in FIG. 5 (also referred to as aconfiguration A), and a semiconductor device having a configuration inwhich the transistor 533 and the resistor 534 illustrated in FIG. 5 arenot provided and the node N55 is electrically connected to the gate ofthe transistor 536 (also referred to as a configuration B).

The operation of each semiconductor device was verified. Theverification results are illustrated in FIGS. 13A to 13C. FIGS. 13A to13C are graphs illustrating the transient characteristics of thesemiconductor devices to which a predetermined voltage input. In FIGS.13A to 13C, the horizontal axis represents the time when a predeterminedvoltage is input to the semiconductor devices, and the vertical axisrepresents the value of a voltage applied to the power supply voltagegeneration circuit 504. Note that the verification was performed here onthe assumption that the input voltage was 10 V, the antenna circuit 501was connected to an AC power source with a constant value, and the powersupply voltage generation circuit 504 had a constant load. As acomparative example, the operation of a semiconductor device from whichthe protection circuit 503 illustrated in FIG. 5 is removed (alsoreferred to as a configuration C) was verified.

FIG. 13A illustrates the transient characteristics of the semiconductordevice with the configuration A, FIG. 13B illustrates the transientcharacteristics of the semiconductor device with the configuration B,and FIG. 13C illustrates the transient characteristics of thesemiconductor device with the configuration C. The results show that inthe semiconductor devices with the configurations A and B, an increasein the voltage applied to the power supply voltage generation circuit504 is suppressed even when time passes, as compared to in thesemiconductor device with the configuration C. Consequently, it is foundthat in the semiconductor devices shown in this example, the protectioncircuit prevents application of a high voltage to the power supplygeneration circuit.

This application is based on Japanese Patent Application serial no.2010-019183 filed with Japan Patent Office on Jan. 29, 2010, the entirecontents of which are hereby incorporated by reference.

1. (canceled)
 2. A semiconductor device comprising: a rectifier circuit;and a protection circuit comprising: a first transistor; a secondtransistor; a rectifier element; a first resistor; and a secondresistor, wherein an input terminal of the rectifier circuit iselectrically connected to one of a source and a drain of the secondtransistor, wherein an output terminal of the rectifier circuit iselectrically connected to one of a source and a drain of the firsttransistor and a first terminal of the second resistor, wherein a secondterminal of the second resistor is electrically connected to a terminalof the rectifier element and a gate of the first transistor, wherein theother of the source and the drain of the first transistor iselectrically connected to a terminal of the first resistor and a gate ofthe second transistor, wherein a semiconductor layer of the firsttransistor includes silicon, and wherein a semiconductor layer of thesecond transistor includes an oxide semiconductor.
 3. The semiconductordevice according to claim 2, wherein the semiconductor layer of thesecond transistor comprises at least one of indium, gallium, tin, andzinc.
 4. The semiconductor device according to claim 2, wherein a bandgap of the semiconductor layer of the second transistor is equal to ormore than 2 eV.
 5. The semiconductor device according to claim 2,wherein a carrier concentration of the semiconductor layer of the secondtransistor is less than 1×10¹⁴/cm³.
 6. The semiconductor deviceaccording to claim 2, wherein the semiconductor layer of the secondtransistor comprises a crystalline region including a c-axis aligned ina direction perpendicular to a surface of the semiconductor layer of thesecond transistor.
 7. The semiconductor device according to claim 2,wherein the rectifier element is a diode or a diode-connectedtransistor.
 8. The semiconductor device according to claim 7, whereinthe diode-connected transistor includes an oxide semiconductor.
 9. Thesemiconductor device according to claim 2, further comprising acapacitor, wherein a first terminal of the capacitor is electricallyconnected to the one of the source and the drain of the secondtransistor, and wherein a second terminal of the capacitor iselectrically connected to the input terminal of the rectifier circuit.10. A semiconductor device comprising: a rectifier circuit; and aprotection circuit comprising: a first circuit comprising: a firsttransistor; a rectifier element; a first resistor; and a secondresistor; and a second circuit comprising: a second transistor, whereinan input terminal of the rectifier circuit is electrically connected tothe second circuit, wherein an output terminal of the rectifier circuitis electrically connected to the first circuit, wherein a terminal ofthe second resistor is electrically connected to a terminal of therectifier element and a gate of the first transistor, wherein one of asource and a drain of the first transistor is electrically connected toa terminal of the first resistor and a gate of the second transistor,wherein a semiconductor layer of the first transistor includes silicon,and wherein a semiconductor layer of the second transistor includes anoxide semiconductor.
 11. The semiconductor device according to claim 10,wherein the semiconductor layer of the second transistor comprises atleast one of indium, gallium, tin, and zinc.
 12. The semiconductordevice according to claim 10, wherein a band gap of the semiconductorlayer of the second transistor is equal to or more than 2 eV.
 13. Thesemiconductor device according to claim 10, wherein a carrierconcentration of the semiconductor layer of the second transistor isless than 1×10¹⁴/cm³.
 14. The semiconductor device according to claim10, wherein the semiconductor layer of the second transistor comprises acrystalline region including a c-axis aligned in a directionperpendicular to a surface of the semiconductor layer of the secondtransistor.
 15. The semiconductor device according to claim 10, whereinthe rectifier element is a diode or a diode-connected transistor. 16.The semiconductor device according to claim 15, wherein thediode-connected transistor includes an oxide semiconductor.
 17. Thesemiconductor device according to claim 10, wherein the second circuitcomprises a capacitor, a terminal of the capacitor is electricallyconnected to one of a source and a drain of the second transistor.
 18. Asemiconductor device comprising: an antenna; a rectifier circuitelectrically connected to the antenna; and a protection circuitcomprising: a first transistor; a second transistor; a rectifierelement; a first resistor; and a second resistor, wherein an inputterminal of the rectifier circuit is electrically connected to one of asource and a drain of the second transistor, wherein an output terminalof the rectifier circuit is electrically connected to one of a sourceand a drain of the first transistor and a first terminal of the secondresistor, wherein a second terminal of the second resistor iselectrically connected to a terminal of the rectifier element and a gateof the first transistor, wherein the other of the source and the drainof the first transistor is electrically connected to a terminal of thefirst resistor and a gate of the second transistor, wherein asemiconductor layer of the first transistor includes silicon, andwherein a semiconductor layer of the second transistor includes an oxidesemiconductor.
 19. The semiconductor device according to claim 18,wherein the semiconductor layer of the second transistor comprises atleast one of indium, gallium, tin, and zinc.
 20. The semiconductordevice according to claim 18, wherein a band gap of the semiconductorlayer of the second transistor is equal to or more than 2 eV.
 21. Thesemiconductor device according to claim 18, wherein a carrierconcentration of the semiconductor layer of the second transistor isless than 1×10¹⁴/cm³.
 22. The semiconductor device according to claim18, wherein the semiconductor layer of the second transistor comprises acrystalline region including a c-axis aligned in a directionperpendicular to a surface of the semiconductor layer of the secondtransistor.
 23. The semiconductor device according to claim 18, whereinthe rectifier element is a diode or a diode-connected transistor. 24.The semiconductor device according to claim 23, wherein thediode-connected transistor includes an oxide semiconductor.
 25. Thesemiconductor device according to claim 18, further comprising acapacitor, wherein a first terminal of the capacitor is electricallyconnected to the one of the source and the drain of the secondtransistor, and wherein a second terminal of the capacitor iselectrically connected to the input terminal of the rectifier circuit.26. A semiconductor device comprising: an antenna; a rectifier circuitelectrically connected to the antenna; and a protection circuitcomprising: a first circuit comprising: a first transistor; a rectifierelement; a first resistor; and a second resistor; and a second circuitcomprising: a second transistor, wherein an input terminal of therectifier circuit is electrically connected to the second circuit,wherein an output terminal of the rectifier circuit is electricallyconnected to the first circuit, wherein a terminal of the secondresistor is electrically connected to a terminal of the rectifierelement and a gate of the first transistor, wherein one of a source anda drain of the first transistor is electrically connected to a terminalof the first resistor and a gate of the second transistor, wherein asemiconductor layer of the first transistor includes silicon, andwherein a semiconductor layer of the second transistor includes an oxidesemiconductor.
 27. The semiconductor device according to claim 26,wherein the semiconductor layer of the second transistor comprises atleast one of indium, gallium, tin, and zinc.
 28. The semiconductordevice according to claim 26, wherein a band gap of the semiconductorlayer of the second transistor is equal to or more than 2 eV.
 29. Thesemiconductor device according to claim 26, wherein a carrierconcentration of the semiconductor layer of the second transistor isless than 1×10¹⁴/cm³.
 30. The semiconductor device according to claim26, wherein the semiconductor layer of the second transistor comprises acrystalline region including a c-axis aligned in a directionperpendicular to a surface of the semiconductor layer of the secondtransistor.
 31. The semiconductor device according to claim 26, whereinthe rectifier element is a diode or a diode-connected transistor. 32.The semiconductor device according to claim 31, wherein thediode-connected transistor includes an oxide semiconductor.
 33. Thesemiconductor device according to claim 26, wherein the second circuitcomprises a capacitor, a terminal of the capacitor is electricallyconnected to one of a source and a drain of the second transistor.